I used to play a lot on both, now stick to FT.
For a lower stakes player (mostly play $1-$5 sngs) there is no comparison- the promotions FT run have made me more than playing there!
Pokerstars are ok, but no rakeback, points are pretty useless (enter a $2k with 50 points and there's over 2k players!) and promotions are almost non-existent/ badly thought out
In terms of software I think Carbon is the best (have recently started playing at PKR- it's awful!!)
overall FT because of the promotions is the best site by miles imho