I really love to play magic type classes, usually ones that can heal, attack with different elements, and have great speed and agility although I won't be able to find that many mages who have speed and agility.
Mostly it depends on the game. But usually I gear towards the DPS type or your basic knight/warrior type. I like Archers too, they are fun sometimes. You don't see them often, but when I do, any kind of summoning type class, or even a class with a pet, that's my first and foremost choice. My favourite class of all time is the Captain from Lord of the Rings Online, He's mainly a DPS but get's a Herald (Pet), and has a handful of buffing skills. I love him cause he's a great addition to any group, but isn't the one being heavily relied on or the most important player in the group lol.
I usually focus on the classes that deal damage through physical attacks, don't have much of a use for energy/mana and have a substantial amount of health to back themself up.
Archer or mage type. Archer because sometimes if i'm doing something important and I don't want to risk death, it's good to be at long range. Mage because casting spells are awesome
I usually go for some kind of barbarian. Something that carries around a large club/mace and has a lot of strength. In games I tend to have an "attack first, explore later" mentality, so in group settings I'm usually the one to go in first and do a lot of damage.
I love to mages / magicians because 1) they normally have long ranged or varying ranged attack, 2) they have a large variety to choose from (usually), 3) they have many mystical effects and usually cool animations and finally 4) I'm not much of a physical person in real life, so I prefer the non-physical characters in games, too.
I don't often play RPGs, but whenever I do I normally pick the fighter/assault class. I like to go out there and start fighting, but sometimes it's good to be the other classes and be patient, especially if there are a lot of enemies around. A fighter type isn't going to survive all of that. Sometimes I'll choose the magic/mage class or elf-type classes, whoever shoots arrows and those ranged weapons. My favorite RPG game is definitely Champions: Return to Arms (I think it's an RPG game). I played this game to death when it first came out on the PS2 and I never did complete it (someone deleted my save files for the game since I shared my PS2 with a sibling, so I didn't feel like restarting all that stuff back then...I probably put about 40 hours of gameplay into this game, so I was a tad upset). I chose the barbarian class for one save then the high elf class for another and it was very fun, especially since you could play co-op.