There is, almost by definition, no universally best pool. Here's a couple of reasons why:
1. User requirements differ wildly: pool hoppers are interested with proportional pools (which non-hoppers should best avoid unless they know what they're doing), some users are
merged-mining hostile and might avoid merged-mining enabled pools. Some users prefer low variance in their earnings while others don't mind the variance at all.
2. The network round trip times to the pools vary on location and ISP basis. Greater round trip times result in more stale shares.
A pool which works for me in Europe might suck for an American user.
The pools I've had good experience with include Eligius, BitMinter, Eclipse and BTC Guild. A few great pools have fallen (MMC, Minecoin), others have declined (ArsBitcoin).
Take a good look here:
https://bitcointalk.org/index.php?board=41.0 
