I always played as the harlequin in Assassin's Creed: Brotherhood's multiplayer mode. I just thought he looked cool, you know, with all of the flipping... and jumping... and cartwheels. Plus murdering! Murdering is cool.
OK, fine, I just really liked the cartwheels. I've never been able to do one myself and... video games are all about letting people do what they'll never be able to do right? Jeez lay off me.
Good news comes in the form of the Assassin's Creed Developer Q&A above though. According to Revelations Community Developer Gabe Graziani, players will be able to customize more than their outfits:
Some of the customizations we've already announced include weapon and apparel changes beyond those we had in Brotherhood, not to mention the ability to customize the appearance of your kills *weird eyebrow movement*