You can't be sure you are getting more from 0% fee pool than from 2% fee pool without comparison on a lengthy intervals. The pool operator can skim blocks (there is no free launch :), pool operator can implement protocol inefficiently and give identical getworks to multiple clients, pool can get a lot of invalid blocks due to bad connection to bitcoin network, pool can get a lot of stale shares.

Unfortunately, to this time nobody did a proper comparison of pools according to their published statistic, so you can only use your intuition to choose one.