The bitcoin you get also varies according to the number of users in a pool. More members means less bitcoin.
I use deepbit as backup while i mine in slush. In deepbit(0.04000) i get less for same hashes than slush(0.06000). Reason deepbit has more members & the mined coins divided to more members than in slush.
I also tried with mineco.in, where i get more bitcoins/block than slush ~0.2234, but when i get coin is the question.