After Bitminter and slush, Bitparking would get my vote. They don't pay tx fee rewards, but offer 3 merged mined altcoins.
Bitparking also pays for orphans. This is what the transaction fees go towards - keeping an orphan buffer. If the network has averaged 1% orphans in the last 12 months then the 1.5% fee at bitparking is really only 0.5%. Add to that the income from the alt coins and the fee is negative. Disclaimer: I'm a tad biased...