I can't really seem to find any information about viabtc offering FPPS, only PPS and PPLNS.
Viabtc offers PPS+ which is the exact same as FPPS, ignoring which order of letters makes the most sense, they both mean you get paid per share and miners (you) keep the fees, keep in mind that most pools if I am not mistaken (including Viabtc) pay the fees in PPLNS and not PPS, but the block reward itself is paid in PPS structure if anything remains unclear google or ask.
With about 6 Exa hashes per second, Slush finds +10 blocks a day, so they do more than daily payments.
Some people like myself look for PPS pools, not for the daily payouts alone, internet, and power stability are huge factors in determining what payment method one should use, I have used Slushpools with a few gears I had in a place with stable internet and electricity and I can safely assume it's one of the best if not the best PPLNS pool out there.
Edit: Slush pool uses a modified version of PPLNS, it's not like most other pools, but it's more PPLNS than PPS.
I would like to add a slight clarification.
PPS+ and FPPS are not exactly the same.
PPS+ means that the block reward will be paid theoretically but the transaction fee will only be paid when they find a block. This also means that your rewards will vary slightly as the transaction fee will differ between each block.
For FPPS it will pay the block reward AND the transaction fee theoretically. How each pool calculates the “theoretical” transaction fee will differ. At NovaBlock, we take the average over the past 24 hour period to ensure it is fair.
This is why you could find some discrepancies between earnings in pools everyday.