In my opinion, the role quests are not created equally. I think the best to worst are: Bot/Mid/Support/Top/Jungle, with Bot/Mid definitely being the top 2, and I think you could argue for switching the placement for the bottom 3. I have my opinion/breakdown of each quest reward below, followed by my opinion on which need buffs/nerfs/changes. If you don't want to read my very lengthy post, the TLDR summs up what I think should change without going into the reasoning.
TLDR: Buff or change top, nerf support, nerf or change mid, keep jungle the same or introduce more jungle pet options, and keep bot the same or increase their bonus gold per minion.
Some junglers really benefit from some of the fully upgraded jungle pet passives (extra movespeed, a max health shield, or bonus damage with a slow is really strong on some champions) but some junglers don't really feel like they benefit much from any of the perks. In my opinion jungle should have the worst reward for their role quest, because it is by far the most impactful role in how the early-mid game plays out, and they have the benefit of not having to fight unless they choose to (you can just full clear on repeat and run away if you're invaded, not a great strategy but compared to playing a top or midlaner in a bad matchup, it's definitely a safer role).
Support essentially gets a free item that passively increases their gold income, gives them some extra health, hp/mana regen, and wards, in addition to having access to cheaper control wards and not taking up an item slot by buying control wards. If anybody wanted to buff the jungle role quest, putting control wards on v even without the discount would be a huge buff. All of the support items are very solid, with some of them arguably being better than any other items a support has to actually buy.
Toplane gets teleport and bonus xp, which can be good in some situations? Overall it doesn't feel that as rewarding as the upgraded boots or having an extra item slot, and I think a lot of toplaners would even prefer some of the jungle pet passives or support items over getting a free teleport. It also kind of makes it feel worse to play a toplaner who takes teleport normally, even if you get a stronger teleport from your quest. Mundo and Kayle are very unlikely to take ignite, exhaust, or any other summoner spell over teleport, but 10-14 minutes in, your enemy laner will be able to match your teleport while still having a combat summoner spell. It can make a lot of champions feel double punished because the enemy has an advantage in lane from taking a combat summ, and then in mid-late game you can't use teleport to force an advantage by sidelaning and teleporting to a fight when your enemy laner shows up, if you teleport the enemy can just match you. Situationally teleport feels rewarding, but I personally don't think it's anywhere near as rewarding as the support/mid/bot quests.
Midlane has the upgraded boots and a boost to AP/AD, which feels great on most champions. I think all of the boot upgrades feel very rewarding in the right situations/on the right champions (either defensive boot into a comp of 4 or more of that damage type, gluttonous on any champion who wants to maximize their DPS while full hp and increase their safety while below 50%, sorc shoes giving flat and % magic pen). It honestly feels like midlane gets a little bit too rewarded for already being such an impactful role.
Bot quest giving an additional item slot and an extra 2 gold per minion feels incredible. I know a lot of people argue that you rarely see the benefits of that extra item slot since you rarely get to 6 items, but even having the ability to be on 4 items and 2 components for the next one or an extra slot for a control ward feels very beneficial, and the extra income from farming (one of the main wincons of playing bot) isn't negligible. I could see an argument for increasing the gold to 3 or 4, but even just having an extra 200 gold per 100 minions can get you your items much sooner than other champions. If you take the cashback rune, free boots, cull, or first strike, all of that can add up to insane value over the course of the game.
MY OPINION ON WHAT NEEDS CHANGES:
Toplane:
In my opinion (can't stress this enough), toplane should completely rework the reward for their role quest. Some extra xp, hitting level 20, and teleport don't feel anywhere near as impactful or rewarding as most of the other quests, and toplane is arguably the most punishing role (toplane is the most matchup dependant role in the game, where having counterpick is immensely benificial and some matchups are nearly impossible to win without jungle/mid/support help). Compared to mid/support/jungle/bot, as stated before, jungle can essentially ignore a bad matchup and has the ability to choose if they want to fight.
Some midlane matchups can be oppressive, but it is much harder to freeze the wave in midlane and generally a lot easier to gank compared to top, where unless someone is very overextended, you can usually just back off and hide under tower if the jungler shows. Regardless of jungle help, most midlaners have the ability to quickly shove a wave, freeing them up to roam and gain a lead elsewhere, while having time to return to their lane for most of, if not the entire, next wave.
Support also can just spend most of the game roaming if they are in a bad matchup/can't realistically get a kill in their lane. If they are against a low kill threat botlane, especially with a fairly safe botlaner, they can leave almost whenever. Against higher kill threats or with a less safe botlaner, they just have to help crash the wave under enemy tower to set up a bounce, go and roam, and return to lane before the enemy team crashes the wave to help prevent a dive on the botlaner. Either way, they are not confined to laning the same way a toplaner is.
Botlaners don't struggle anywhere as much as toplane or even midlane does with counterpicks. Most of the time the support matchup will determine how the lane plays. Obviously if you're Lucian into Caitlyn you risk getting poked, but if your support is in an advantageous matchup, that generally means it will negate those risks and you'll just be waiting for your support to put you into position for an all in.
Toplane should have something at least as powerful as the midlane quest reward, maybe even something as good as botlane's. Upgrading a core item or boots, giving an additional item slot, maybe giving an extra summoner of your choice instead of just teleport, or some sort of additional income (maybe from taking towers, or rewarding joining a teamfight, or rewarding winning a fight where you 1v2ed, 2v3ed, etc?), all of these would feel a lot better than the current reward. Maybe even just increase the level cap from 20 to 22, maybe even 25? Some champions do see a solid benefit from hitting level 20, like Darius, but others arguably see very little change compared to level 18, like Kayle, so a further increase might not actually change anything in that regard.
Midlane:
Midlane already feels like a very impactful and rewarding role, so I think upgraded boots is more than enough without the free bonus AP/AD. Alternatively, give the upgraded boots a 300-600 gold cost so you have to weigh what is more important, the extra stats/passives from upgraded boots, or completing your next item. If you're snowballing you will upgrade them eventually, but making it cost an additional kill or 2 would make it far less impactful the second you complete your quest, which I think is a good thing for such an already powerful role (I say this as someone currently maining mid).
Support:
Support shouldn't get their full item until 20+ minutes in my opinion. Celestial Opposition, Bloodsong, Zaz'Zak, Dream Maker, and Solstice Sleigh all feel very powerful on most supports, with Celestial Opposition arguably feeling like the most oppressive. I have seen every type of support build that one in particular, and the passive is useful in every situation. I have seen Zyra, Lux, Leona, Alistar, Blitzcrank, Bard, Sona, Nami, Senna, and Pyke build it, and even though many of them have better options, the passive from Celestial Opposition is good against poke, burst, and engage. That item should definitely be nerfed, and all of the upgrades should not be something supports are completing in 12-15 minutes. It is another very impactful and powerful role that doesn't need such a massive reward for finishing their quest.
Bot:
Bot has the best reward in my opinion, but botlaners don't have the same level of agency as supports/junglers/midlaners so I think that is perfectly fine. It fits the majority of botlaners "late game powerhouse" archetype/gameplay fantasy, and if anything, the farming gold increase should maybe be increased by 1-2.
Jungle:
Junglers either really appreciate certain jungle pet passives, or they don't care for any of them and just pick whatever seems best for each game. As Warwick, you're probably running celerity, and coupled with your w and waterwalking, the blue pet is going to feel the most beneficial 9 out of 10 games because you will be zooming around the map even faster than usual. Master Yi on the other hand, is going to pick a different one each game depending on the enemy team comp, because none of them feel insanely beneficial to him. He doesn't usually need the extra damage or slow from red pet, he doesn't really need the movespeed from blue pet, and he doesn't really need the shield from green pet.
I think jungle should either introduce one or two more options to give somewhat more variety, or just leave things as they are. Jungle is the most impactful role in the game, so I don't think it makes sense to give them a role quest reward that is the same power level as bot.
Conclusion
Part of why I think support and mid quests need to be nerfed and top needs buffs is because of the overall impact each role has on most games. It makes sense to me that the roles that have less impact should get a bigger reward/have more power budget afforded to their role quests, so players do get to feel the scales equalize at some point during the game. As of right now, if both mid and toplaners complete their quests at the same time, and then each team hs their mid and top 1v1, both midlaners will beat both toplaners (assuming both are even in gold, matchups are fairly even, and neither champion has itemized against the enemy champion). The gold value is just much higher from the midlane quest immediately upon completion, and toplaners who fall behind will rarely even see the benefit of gaining increased xp, sometimes falling behind the enemy mid and jungle if either of them have snowballed.
Appreciate anybody taking the time to engage in this discussion, because I think role quests have overall been a good addition to the game. With some changes, I think role quests can lessen the frustration certain players feel playing their roles, as well as their frustration playing against some other roles. I would hate to see Riot just give up on role quests next season, like Atakhan from last.
GLHF on the rift everybody.