FTP sucks IMO.
FTP has less traffic, higher rake at the micro limits (especially if you don't have rakeback), their customer support sucks, and I've experienced a lot of trouble trying to cash out money with them (I'm in the US and know that many other players have had issues lately).
PS has MANY more players, lower rake at the micros (anything below 25NL), better filters for cash games, and I have NEVER had a problem cashing out funds from that site. Since I have never had problems with their site or money issues, I have never had to deal with their customer support. So I can't give you an honest rating for it.