Nanopool and Ethermine are both good pools. My earlier post I was just suggesting a pool other than ETH pool, but nanopool is just as good so if you are already mining there don't sweat it. As far as the variation all pools have what is known as Luck or streaks where they might find more or less blocks per a given time period (say 1 day) than is average. So trying to compare two pools on short time-frame will not work. If you were to point equal hashrates at both pools for a month you would see the payouts would be nearly identical. The fees and what they pay on may vary, but they usually offset enough that in the end the profit is the same.