I think the guys in the "NPC Natural" show at least pretend not to be on anything, while in the regular show its understood most people are
If you are doing it to give you the extra push to be the best you can be, do either show. If you care about winning, and are natural, go with the natural show. I did a a regular show for my one and only stage appearance and was... at a disadvantage to some of the other competitors. Didnt care though really because the show was an "end date" for me to take myself to the limit.