It depends on which console you're playing II on because the Xbox and Gamecube version definately look better than the PS2 version (though III looks better than the PS2 version of II and III is only on PS2).
I've read about III online and am impressed with the amount of characters on there. I do like using Yunsung on II though but it doesn't matter because I could always use Kilik, Nightmare or Cervantes if I ever get to play III (and seeing as I don't have a PS2 then probably not).
In my opinion, Cervantes is the best character in the game. On a side note, is there anyone who can perform the moves that the characters can do (obviously you can't jump up incredibly high like Cervantes but I'm talking about the weapon techniques).