Yeh, if you're a US citizen and into online poker then it's a no-brainer to join both FTP AND PS. You only have a few others; Ultimate (Tight City) Bet; Absolute (Dodgy) Poker; Bodog (Shmodog) and the Microgaming (Scandinavians-Are-Us) network. Oh and the power-house that is Cake Poker
I just joined FTP today (I'm from the UK and only just learnt they accept Maestro) but I find their SnG structure to be excellent. Even though they are only 6 minute levels, the chip increase is actually quite small incrementally; which means you really don't have to play it like it's a turbo.
I have to say, I had great fun trying out the $5 SnGs today - although I could have done without it going down when I was chip-leader with 4 players left!!
And Poker Stars? Well, the tourny choice is great and the software is slick and has nice features but I've personally just not done very well there :-(