i love them both, but the gay alien,roger, in american dad cracks me up. o and hayley, the teenager, is so like me its scary.especially wen she dyed her hair green after i begged my parents to let me do the same. and of course klaus is brilliant.
I think that for most people Family Guy will always win....there's five seasons and the specials and its the original isn't it....I think if you compare the first seasons of the two shows then AD wins hands down. Lot's of porential there!
I guess AD is more un-PC than Family Guy so it can be a bit more of shocking humour and get away with a bit more than FG can....but then again I love how random FG is, there isn't that same sort of thing in AD...it doesnt just suddenly mimic other shows etc randomly.