I have mined on Slush, BTCGuild, 50BTC, BitParking, and BitMinter. I have settled with half of my hashrate on BitParking and half on BitMinter. BTCGuild and 50BTC are steady payouts and you know more or less what you are going to get (BTCGuild gets steady blocks because of it's size so it doesn't feel like there is a lot of variance), but I have no doubt that you get less in the long run than you do on any of the other "high variance" pools I mentioned above. The variance can suck on any of those pools when luck is bad, but in the long run the payout for me has always been more on any of those pools. The reason I don't mine on Slush now is because I just don't like his payout scheme but as I say, still a more profitable pool than BTCGuild or 50BTC.
BitMinter is having some DDOS issues right at the moment though which is a bummer