Tell me what is the best pool ? and how to calculate the complexity of , say if Solrate then diff should be 200,300,400,10000?

Mining
1

tell me what is the best pool ??? and how to calculate the complexity of , say if Solrate 550 s/s then diff should be 200,300,400,10000???
zec.suprnova.cc offers instead of a password to supply Difficulty , but what ? if I solrate 550 s/s from one farm