The "big" difference in plugs is the heat range. This is the equivalent of advancing or retarding the distributor in your car and why I can never understand the blanket statement "use an OS #8" (or whatever) without considering how much nitro is being used or other variables. A hot plug from one brand will be different to a hot plug of another brand so there's going to be a difference in revs. That doesn't mean that one plug is better, it just means it was more suitable to that particular engine/fuel combination. Some plugs (Enya for instance) have a reputation for lasting longer than others but I've found that even some real cheapies can last practically forever.

The basic thing with plugs is that the one that gives the highest revs is the best plug (regardless of brand or heat range).