Both are good social networking website but right now Facebook looks nice because lots of changes are done in that.
There is no comparison... FB for sure. Twitter has lots of Cons like Limited functionality; find people, send brief messages, direct replies, Limited to 140 characters per update..etc. I don't prefer it.
I think both are good but like most of use use facebook more then twitter.. I think a fan page would be the best. would be compareing like Google and Yahoo of course people use google more then yahoo and better traffic.