This is because wafflepool accepts "stale" shares that are one block behind, just not two blocks behind.  Also, you'll have a hard time comparing wafflepool over a short period of time, because they mine the most profitable coins like dogecoin that other profitswitchers won't because their hash rate isn't high enough.  This causes larger day-to-day variance on wafflepool, but based on the law of averages will equate to higher income over time.