Inzer makes a quality belt, and so do Crain and a few others. As far as I know, Inzer's belts are legal in most (if not all) federations. The best way to check if a belt is legal in the federation you compete (or plan to compete) in is to check the federation's rulebook. I do know that some federations will only allow gear (including belts) manufacured by the sponsors of that federation. However I would be surprised to find a federation that would disallow an Inzer PL belt.
My recommendation would be a single prong 13mm forever belt (by Inzer), but a 13mm belt can be a real bitch to break in.