Soul Calibur is a great series. I own them all, but only played Soul Edge (original PSX game) and Soul Calibur (Dreamcast) to death. I've only tried out the other ones, unfortunately. I must get around to playing them sometime, since the short while I played SC2 and 3 was very fun.
I like to use everybody, but my mains are probably Nightmare, Siegfried, Mitsurugi, Voldo, Raphael, Cervantes, Lizard Man and uh...everybody else...lol...
And to clarify, I chose Nightmare as my nickname (not on the internet, though) before Soul Calibur even existed.