I like the "Dondi"-style muzzles because they're nice, sturdy, and not badly priced plus not very easy for a dog to work his/her way out of. The only bad thing is that you have to be careful not to leave some of them out in the sun/rain for any period of time.
They have muzzles specially made for Malis, GSDs, and I believe for Pitts, Rotties, and Mastiffs. The only problem with these is if your dog's nose is slightly longer (or shorter) than the average for your breed. The best thing is to find one made for your breed, order it from a website with a return guarantee, and give it a try. Worst case would be having to have one customized/custom made for your dog.
As far as muzzle fighting (which I haven't done in years) I always used to use the Dondis with reinforced sides.