I only use feat. in the song titles if there's different versions of the song. For example, there's a version of "Booty" featuring Pitbull and one featuring Iggy, so I have them labelled as "Booty (feat. Pitbull)" and "Booty (feat. Iggy)", respectively. "Get Right", "Get Right (feat. Fabolous)".
I used to use ft. but over time I didn't like the way it made my tags look, especially since iTunes always used feat.
So now I just use feat. and I try to keep my tags as close to iTunes as possible, unless it screws up the way my music is scrobbled on Last.fm or there's blatant errors in the way something was tagged