Rufus and Squall are already done, so I can't really recommend doing them. Sephiroth is already accounted for(by two people already actually), so I wouldn't do him either. If there's a free character you'd like to do, though, I have no problems with that. You can check the character list page to see who is done, accounted for, and still open.

As far as how you draw it, I'm fine with freehand, as long as it is in something like ink or marker. I can take pencil-drawn and colored art, but it doesn't show up very well with the rest of the characters, so I'd stay away from that if at all possible.