Well there are a few different places that give suggestions.
https://bitcoinfees.21.co gives a suggested 240 sat/byte
https://blockchain.info/charts/mempool-state-by-fee-level suggests 5sat/byte for a "normal" transaction, and 200 for a priority one.

That's why it really helps to know what the ...

Between... https://bitinfocharts.com/comparison/bitcoin-transactionfees.html#3m
and https://bitinfocharts.com/comparison/transactionvalue-btc.html#3m
you should be able to take the value of how much was moved per day, how much was spent on transaction per $ moved, and come up with a number for a ...