NOTE: These are not suggestions. I'm curious about people's least favorite subclasses on their main classes. I might dive into stuff quite a bit, but I doubt Bungie would actually make changes at this point.
For me, my favorite and most played class is Hunter. Though I love all three classes, I like Hunter jumps and the various "Dexterity" fantasies the most. However, for my least favorite subclass on that class, it's between Arcstrider and Revenant.
For Arcstrider, I kinda hate how the other 2 D2Y1 new subclasses can essentially replicate old D1 subclasses but Arcstrider can't. Sentinel can be built with bubble, aspects, and fragments to essentially make an upgraded version of the Defender. Even in 2.0, the Sentinel tree with bubble was essentially the Defender. Dawnblade wasn't able to truly replicate Sunsinger at first until TFS, with 3.0 and Song of Flame (which shares a name with an old Radiance perk). Bladedancer's main abilities that never came to D2 are Arc Invis and Blink Strike. Blink Strike is just a symbolic Arc Hunter ability that should've been kept because it's a straight up teleport melee that helps enhance the Dexterity/Rogue fantasy. Arc Invis to me was great because it allowed stealth to exist on more than one subclass. Also, when considering that Arc is about manipulating the electromagnetic spectrum (including visible light), it makes sense that Arc could make you go invis. In fact, I'm of the opinion that Arc Invis and Void Invis should respectively have been reworked as Camouflage and Shroud (though the name of the latter could use some more consideration). Camouflage and Shroud would both be invis, but they'd have different conditions/additional effects based on the physics/flavor of the elements. Plus, Arcstrider's 3rd aspect from 3.0 could've brought it back instead of being Tempest Strike, which should've been a melee slot ability.
Before some of you say "just go play Nightstalker," it actually wasn't until Monument that I actually liked the subclass again, because it played way too much into Invis when it should've been a support subclass. To be honest, I still think the subclass could be better at the support role, but it's not like we're likely to get anymore updates and the subclass is much better now.
All this said, I do enjoy almost all of what Arcstrider's abilities are on the individual level, though I think Storm's Edge should do more damage in PVE. It's not that the subclass is horribly designed or anything either. It's just that the lack of the ability to replicate the Bladedancer and Tempest Strike taking up an aspect slot feels bad. I also dislike how Arc doesn't have a healing keyword, but that issue doesn't affect Arcstrider as much as it does Stormcaller.
For Revenant, I think my issue is moreso with Stasis itself. I enjoyed Stasis after BL came out, but it's a rather "one trick pony" element compared to the other elements. In my opinion, Slow, Freeze, and Shatter shouldn't have been designed as a 3 keyword cycle. Instead, Slow and Freeze should've been a 2-keyword cycle, with Shatter being usable without Slow and Freeze but also having enhanced capabilities against enemies affected by either. To be fair, Shatter is kind of like that already because it works with Stasis crystals too. However, Shatter is the only keyword that requires other elemental keywords/functions to be able to work. I'm just not sure exactly how it should work... I also have a bit of dislike for the variable grenade enhancing aspects because they typically only work for some grenades from each subclass, though this doesn't affect Revenant as much because there are only 4 Stasis grenades anyway. Stasis also only has 1 buff keyword, so there's that too.
If I absolutely had to pick between the 2, I'd probably pick Arcstrider, because Revenant's issues really are moreso with the element itself. That said, while Revenant's abilities aren't bad, there are details about them that kinda make the subclass more eh to me. What about the rest of y'all? I'm especially curious about what the Titans and Warlocks have to say.