I prefer recurring. Just because I have members that have been on my paysite since 99. I know how nice that recurring can treat you after a year of steady promotion. I make $200 a month recurring on AVS Premium sites that I haven't updated in years. Plus, I always feel like I'm going to get shaved if I pick pay-per signup. Damn, I wish I wasn't paranoid.
But it does depend on the site. I update my paysite members area with exclusive content I shot myself 2 times a week, and have daily leased gallery updates, so my members stick around.