Liftoff is fun, I've always recommended FPVFreerider for serious training, it's more stripped down and focuses on absolute core flight functionality. Less tuning, more flying.

The graphics are basic but that means you'll never drop a frame even on a potato at 165Hz, the flight controls are insanely tight. Likewise this was the software I paired my radio with and learned to fly.

It's also only a couple bucks and there's a freeware/demo version floating around out there too.