There is no one bit that is the best. It comes down to the horse and what THAT horse needs. Most of mine will run in just about any bit. I tend to like one with a higher port as it give more of a single to the horse with very little movement.
I agree it definitely depends on the horse.
My mare liked to gap at the mouth because of other issues, and we finally found a bit or two she was good in so those are the ones we started showing in.
For my mare (remember this is specifically for her).
I love to warm her up in a correction with a medium port. And my favourit bit to show her in is a lower port than that, we have two that a similar and she goes great in them.
We tried everything on her, high/medium/low port, spoon bit, c-port. We play around till we found stuff she liked. And then we didn't use it to show in.
My show bit is pretty much the bit I put her on and start to warm up and then go show. Not the one I ride on an every day basis, especially not at shows.
But you really just need to play around with it and figure out what works for your own horse.