Depends what your goal is...to make money then I would say both...just to communicate with friends I would say Facebook.
right now im with facebook. Until twitter update themselves and add some new features they will not be able to beat facebook.
Personally I think they're targeted for different types of users. Facebook seems more so for people who want to connect with other people on a personal level; like with friends from school. Twitter, on the other hand, seems more so useful for people who want to follow the latest developments of a business; like if Sony decides to hold a contest, they can tweet it and fans can follow. That's just my personal impression though.
If you want to advertise something than twitter is a good way but if you are a serious user on twitter than it's kinda sucks as you'll have tons of spam coming to you all the time..
Both provides No follow links. They can send visits only. Facebook is better, you can post images and more texts. You can share with your friends. ...
Twitter is more powerful just because of the number of users, but at the same time it's become a sespool of marketers to the point where if you're trying to market your own product, you're only promoting it to other marketers which is about useless. Twitter's become a feeding frenzy of spamming to other spammers lol Facebook takes my vote.