I'll give a short run down of the melee.

Dragoon
Arguably the most straight forward, offering extremely high rDPS and decent pDPS. The rotation itself is quite rigid, making the job easier to pick up but does lack in flexibility. There really isn't much downside to Dragoon save little annoyances like Piercing Talon being completely worthless due to Raiden Thrust's existence. Perhaps it's only "hard" aspect is learning the best ways to min/max.

Ninja
While the weakest melee, it does boast significantly high rDPS and surprisingly high burst. Unlike Dragoon, the rotation is incredibly fluid—making it the only melee truly capable of occasional range combat without hindering itself. That said, it is quite a "busy" job, especially in the opener. You have quite oGCDs you ideally want to keep in sync otherwise you'll wind up losing a usage. I'd say it's probably the least beginner friendly but wholly satisfying to play once you get passed that learning curve. If you've played Dancer a lot, the new mudras will feel similar to your Steps, which may make it easier to pick up.

Samurai
Sort of in the middle between the aforementioned two. You have more flexibility than Dragoon but nowhere near what Ninja offers. Since you're only concerned with dungeons and the like, I'll skip what makes Samurai a bit... awkward. In that setting, you'll find it plays quite similar to Dragoon; rigid and straight up. It has no utility to speak of but deals huge damage all up front. With only a 60s dot to really think about. Samurai is what I'd call "comfy."

Monk
Admittedly, I dislike Monk. The rotation feels a bit boring, especially as it has virtually no oGCDs. It does nearly as much damage as Samurai while offering good utility, but I find... nothing flows. So much of the job feels at odds with itself. Anatman is just... bad; Tornado Kick is worthless. You'll find yourself spamming the same handful of buttons a lot. Of course, I'd still say give it a shot. There are things to enjoy about Monk. And it's not too difficult to pick up. I simply can't recommend it myself.

As for AoE, they are all good choices. Dragoon is the strongest but even Ninja can be a straight monster once you learn all the ins and outs. If you're wanting to get your feet wet without feeling too overwhelmed, I'd go with Dragoon or Samurai first.