I've gotten both a hero and kaiser to 200+. Kaiser is different, it's really something you have to play to see if you like it. Hero was my first and only for many years, they are easy & fun to play & train with, and probably the "strongest" (they hit harder with less funding), but I found they are lacking when it comes to bossing & DPS (due to lack of lines). Their 1v1 (bossing) skill is actually a buff, instead of it being a separate attack like most classes. So it makes it difficult, for instance, when trying to kill gollux and having to toggle this thing on and off to try and kill the minions at the same time, especially when each time you use it it consumes some of your orbs.

Kaiser is a bit more involved, but it's pretty fun too. Annoying to mob with, but I personally loved it. You can play it kind of like an Aran where you combo up moves to do certain attacks, OR just assign all the attacks to a key like normal. Combo'ing fills up your gauge quicker though, which lets you transform into the dragon form -the ONE thing I don't like about it and the only reason I don't play it. You can transform into the OP dragon every so often (which also ignores DR), but movement is limited. Sure you can tele unlimited distance in any direction, but you can't jump. It's just something that really bothers me, especially for trying to kill Cvel... but hey if you don't plan on trying to do that, then you might love it! They do have the best potential for most DPS because their main attack does a crazy amount of lines.

Drk's I have no experience with, but from what I hear they are better at bossing than hero's.

...and now I am a paladin... because I just love not dying more than anything, and I have the funding to be pretty op as well. :3