I also have the Mayflash adapter along with a number of other controllers: the Classic Controller, Classic Controller Pro, WiiU Pro Controller, 8bitdo SNES30 gamepad, a PSX to Gamecube adapter, and NES to Gamecube RetroPort adapters.
I use original controllers with the Mayflash and RetroPort adapters. Last week, I also scored a rare SNES RetroPort adapter that will be delivered sometime this week.
In my experience, the Virtual Console games are definitely more responsive, which is especially noticeable with platformers like Mario. I also see improvements when using official Nintendo controllers. The most responsive input is from the Classic Controller Pro. I'm not sure if it's the way the adapters send inputs or the way the emulators receive them, but the controls always feel off and ruin the entire experience for me. I'm hoping the direct wiring of the RetroPort solves my issues and I can enjoy using my original SNES control pads. If not, next stop is either moving back to the original console or giving sucking it up and buying the official Super Famicom controller released as a Club Nintendo award.