Here's some Order of the Stick action.
I love Aasimars because I like good things. Angels, Daevas, Archons, and similar good outsiders are super cool to me. Being the descendant of one of them is similarly awesome. I happen to love paladins and clerics, and they make awesome paladins and clerics, they're powerful in the ways of racial abilities (especially in Pathfinder which is my Sword and Sorcery poison at the moment), and there's some impact when you can manifest a glowing halo.
Oh TSR. You somehow make striped/polka dot tights cool...
Tieflings are the descendants of fiends. I love demons and devils and daemons even more than I love good stuff. They also have horns, and I love people with horns (one of the reasons I love Changeling: the Dreaming so much is because Satyrs are one of the kiths). They also, depending on edition, get prehensile tails, bite and/or claw attacks, fire resistance (there is not enough to be said about how awesome it is to stick your hand into a torch to freak people out), and can cast cool spells like Darkness. I also love playing antiheroes or heroes with the odds stacked against them or that people would assume to be monsters before getting to know them. Tieflings fit the bill perfectly.
I'm basically playing this as a Ranger in the current game I'm in.