As I'm in the long game.... i figured I'd keep it simple. Run 30 days on slush. Run 30 days on btc.com. See if there's that much of a payout/earning difference during that time frame (after I take difficulty increase into acct). There's gotta be a reason more miners operate on btc.com than slush. If there's a notable difference, I'll stay with the better payer. If the difference is negligible, I'll go with the easiest to use/understand interface.
I think the more correct test would be to run two identical mining gear against the two pools in parallel, that is, no hopping of those two.
If you have a large group of miners, then you "could" hop those based on that information. Add more miners/pools to evaluate more in real time, and stats will improve over time. A year evaluation is far more valuable than a month, and a day is nearly worthless.
Usually once you find a pool good enough, it tends to remain that way making hopping unnecessary and in fact a waste of hashing time.
Ideally you could just run cgminer's balance mode and dedicate a single unit to this task (and permanently evaluate all the pools you want from it), but i don't know how harmful this switching is. From experience, I'd say its harmful without #xnsub, it wastes too much time switching and the hashrate is impacted significantly. So, multiple (identical) units pointed different pools would be best to have those pools profits properly checked realtime.