i like both for sure, but i think i like giving head more. my penis isn't sensitive enough to like head as much as fucking a pussy or ass, so i'd just fuck if it were up to my penis. but i LOVE pleasing my partner, man or woman. I love eating pussy (can do it all day), and I like sucking a nice big dick to completion.
Another reason to prefer sucking to getting sucked is that getting sucked off and cumming means your fun is over (or it does for me, i lose interest in sucking dick or getting fucked after i cum--but i can still lick pussy...). Sucking, you can stay horny and suck a few buds off before needing to get off yourself.
I guess another consideration is STDs, though. Probably better to be sucked than to suck, especially if you like to swallow.