Brake goes to floor

I have cutless cierra 93 i have changed its master clyinder 6 months ago but since couple month it brake padle goes to floor but don't get even hard when you pump.I took it to mech. one said your brake booster need to replaced other said it is just the master clynder i am not sure what to do.Please help

I know this is a do-it-yourself site but your situation calls for the restoration of your vehicle brakes immediately, as I think you've acknowleged.
Let the one that says master cylinder replacement fix your brakes. Might as well let him check and fix your whole braking system.