Hard to pick a favorite, but i'd say Assassin is in my top 3. I love doing Masterful Kill on enemies, especially bosses. Nothing looks cooler than going ninja on people and cutting their necks, or dodging a huge boss attack and cutting their arms and legs. And with Gale Harness i can get around the map much quicker.
Magick Archer is cool just because they make arrows of magic, reminds me a lot of Clock Tower, or really any media with light arrows in them. Plus it has amazing versatility, i can go from long range, to melee range, to magical AOE attacks whenever.
And i guess my third would be Strider. The cords are too much fun. Also jumping off enemy heads and spinning through the air. Sorcerer would be amazingly cool if i wasnt left so vulnerable, charging up like a DBZ character while creatures wail on me.