This is an interesting question, but also a very difficult one to answer.
No, all pools don't pay exactly the same.
But looking at how much a pool paid out over a few days is pointless due to variance. Another mistake common with beginners is to try to find some magic ratio between your hashrate and the pool's hashrate that will let you earn more. In reality this ratio has zero influence on your earnings. I will try below to tell you what actually influences your mining income in the real world.
The best data currently available is probably the BTC Mining Pool List at Bitcointalk. Note that the profitability graphs at the bottom do not (at the time I write this) take into account pool fees, merged mining and rejected work (the last one being very individual).
Which pool is most profitable to mine for you depends on a lot of factors. I'd say there are two main influences on how profitable a pool will be for you: variance and expected average income.
Variance is determined by pool hashrate and reward system (PPS, DGM, others). The more variance the more luck will influence your profits. The variance tells you how far the income is likely to vary from the expected average over the short term.
Expected average income is determined by a lot of factors, which many miners probably don't realize:
- Which ratio of rejected work are you getting? Some pools have a higher average reject ratio than other pools. On some pools your individual reject ratio may be especially low. Some pools artificially lower your reject ratio by paying rejected work. This is not actually an improvement. It means people with low reject ratio (good setup) are forced to give some of their income to people with high reject ratio (bad internet line, bad equipment).
- What ratio of orphaned blocks does the pool have? (ignore for pps pools)
- What's the average income from a block in the pool? (ignore for pps pools) Some pools will have a higher income from transaction fees. Some pools keep the transaction fees and don't pay them out to miners.
- How much of a bonus do you get from merged mining? This depends on which other coins are merged mined, their difficulty, their current value compared to bitcoin, in addition to all the factors listed here but for the merged coin (average income per block for the pool, orphan ratio for the merged coins, etc.)
- What is the pool fee?
I don't include pool hopping in this list, since most Bitcoin mining pools are not vulnerable to pool hopping. Things may differ in the altcoin world.
There are some factors that are the same for all pools, like bitcoin difficulty, bitcoin value and your expenses, like electricity. Bitcoin mining calculators seem to cover these well, but they don't cover most of the factors above that are individual to each pool.
All of that being said, there's a lot of other reasons for picking a pool than a small difference in mining income.