They should pay roughly the same. Deepbit is generally favored as paying slightly more last I checked (this was mostly due to a higher stale rate on Slush's pool, which is no longer a factor [AFAIK] after a significant infrastructure overhaul), and it is theoretically possible for "pool hoppers" to exploit Slush's pool (however, that information is months old -- I am not certain if it's still true).
You may also want to consider Mt. Red @
https://mtred.com/ which does PPS but doesn't charge a fee, as well as Eclipse Mining Pool @
https://eclipsemc.com/ (no fee) if you don't mind short-term variability in how much you're paid. They maintain operation based on donations - so whatever you feel they deserve, they get. It's also generally considered "community service" to mine on pools which are not particularly large, for if a pool were able to secure roughly the majority or more of hashing power, the pool operator would be able to perform what's called a "51% attack" (see
http://gavintech.blogspot.com/2012/05/neutralizing-51-attack.html for what it is and how the devs are working to prevent this situation).
Cheers & happy mining!
ETA: I left out Graet's OzCoin @
https://bitcointalk.org/index.php?topic=14085.0 - which is funny, because I mine there. They share similarities with EMC, but OzCoin better-supports (AFAIK) FPGAs, which I'm guessing isn't really a concern for you.
