I have all 3, not an expert, but will just share my thoughts.
I find Schwab and Fidelity much easier to use, especially in terms of trading.
Fidelity and Vanguard both automatically place all cash into a decent interest bearing account, currently over 4%, in Schwab you have to transfer money into the specific fund with a decent interest rate, their standard sweep account has a very low (if any) rate.