This is a subject I find weirdly interesting for some reason.
I'll go over mine, for anyone interested, in no particular order because I'm terrible at truly ranking things.
Succubus
For reasons beyond my understanding, I do prefer to avoid killing much if possible, and Succubus vibes well enough with that. What with the STD spreading, since if you kill your STD carriers, well, they lose STDs! Being able to pull someone in range to your space and incap them every 6 turns is pretty nice too, simple but very useful. A 5 turn cooldown skill in Fear and a 6 with Seduction also helps prevent the class from feeling too sluggish. Just an old favorite, a class about as old as my account too, IIRC. :o
Illusionist
Conceptually, I've always thought characters like this are really cool. While I tend to dislike RNG ingrained in classes, Hallucination's 50% chance is high enough that it's unlikely a game will leave you feeling like it did nothing. Grand Disappearance is just such an awesome and versatile skill, as well, and I do love anything that can put someone on a very specific chosen space. Magic Hat is very cool too, though I might be biased since I suggested (a much weaker version of) Magic Hat to help this class when it felt pretty underpowered. So that's very cool. @_@
Saboteur
I am so happy for this class, it's come a long way from where it was when I joined. I really like versatility, and this class has that. I really like the more analytical nature this class lends itself to. It feels like it's a lot about being observant and figuring out what's going on with everyone else and how best to respond to that. To me it represents my ideal for all classes in BGO, because what it does, is very distinct and unique to it, you can't really emulate Saboteur's kit, all 3 class skills work in harmony with each other, and the only random component to it can also produce reliable results when used in tandem with another skill. Sabotage being the focal point that connects Hinder's fire and Tinker. The one drawback for me, is, I don't like upsetting people, and boy howdy does this class upset people. >_>
Druid
One of my favorite things to get out of a class, is the ability to do things with the class regularly, and Druid is really...fast with that. Every 2 turns. Technically a little less than that, thanks to Nature's Swiftness. This class is very versatile, and there's a certain flow to it that I hope to one day fully get in the groove of, of how to play it. It's really cool. And another big plus for me, is how self-sufficient it is. It's not a class where I find myself going "I really hope I can get and keep this and that item or this and that event comes up" I mean obviously good fortune and various items help a lot, for any class, but this class' skills feel very self-sufficient, and adaptive, and reliable.
Time Twister
I was unsure for awhile if this fit with the others, but I think my strong desire to better wrap my brain around learning this class so it becomes second nature indicates my fondness for it I already have. It does things no other class can do, and like Lawyer for example, some of these things transcend normal effects. Lock Time, for example, is not something you simply can block, or remove. You can play around it, or even turn it against the TT in some situations, but it's very powerful. And very versatile. Lock Time has a low cooldown, and yet oftentimes in games I find myself wishing it was off cooldown and regretting my last use of it as a better use presented itself. Bend Space is one of my favorite skills in the game, Explosive Sheep is one of my favorite items, and those two things are best friends. But just...an AoE "put other players on this exact space" skill...wonderful. Steady Progression is usually not very strong, but it's a 3 turn cooldown skill so...it better not be really strong. But it can still do strong things, sometimes. Altogether a quicker class too with low cooldowns, so...fun times all around.