It's extremely hard to pick a single class, so I'm not going to (sorry of that's breaking the rules). My three favorite classes, all from 4e, are Paladin, Sorcerer, and Warlord. Generic disclaimer, this is all IMO, YMMV, etc.
Paladin is, for me, the most on-theme version of the class we've ever gotten. Lay on Hands got a version that ACTUALLY sacrifices something, the Divine Challenge and Divine Sanction make a great deal of sense thematically, the class is about being a champion of a deity and not a moral policeman, and it's INCREDIBLY flexible, able to go half-striker, full-leader, or even dabble pretty well in soft control effects.
Sorcerer is just a lot of fun. It feels like a real blaster, like you've got a powerful force inside you waiting to be let out. Chaos, if that's your thing, feels genuinely pretty random, and has all sorts of teleportation and tricksy things. Dragon and Cosmic make you bruisers, the former more straightforward, the latter more complex. Storm is a surprisingly group-supportive striker, and really gives the feel of riding the lightning in the right contexts. And then the Elementalist is the first true, honest-to-Bahamut ACTUALLY SIMPLE caster I've ever seen--much simpler than any version of Warlock ever made. Sorcerer has something to offer to almost anyone interested in being a heavy hitter (as long as you aren't allergic to being openly magical).
Warlord...it's the epitome of 4e design. Excellent support class, made it not just useful, not just fun, but AWESOME to support people. It isn't just a Brother Bactine, it's a **-kicking, force-multiplying powerhouse. It recognizes that every mental stat--Int, Wis, *or Cha--can be useful for leadership in the right context, and toward the latter half of 4e's run, it could genuinely support a mostly or entirely "Lazy" build if that was your thing (though that really wasn't its best performance, just an option permitted, eventually). While it couldn't be relied on to bring mega heals like a Cleric, it could do all the basic support concepts a full-support class should do, hence people called it a "full Cleric replacement."
If I had to pick a favorite Controller...I dunno, I wasn't as well-versed with them as the other three roles.