I use a ShockDoctor 1.5 because that brand happens to fit me and is comfortable.
But if you are fighting then ideally you should have one made for you by a dentist. The max fax surgeons at work (the ones who deal with damaged jaws and teeth) say that a custom made one will disperse the forces of a blow evenly. A 'standard' guard won't do that, which means that you can actually end up with more damage as pressure can get concentrated in one area.
As I progress I intend to get one made for me; in the UK it should cost £50-£100 and will last for years until your mouth or teeth change.
