Powerlifting, to get as strong and build as much muscle as possible. Practice and train specifically for the event. Then, I guess you could cut down and do the bodybuilding show.
But, to me, it seems that there's a big difference between entering a strongman/powerlifting comp and entering a bodybuilding show. Even with your limited experience, you could probably find a strongman or powerlifting comp that you could enter this weekend and compete in a division where you wouldn't be totally embarrassed. In fact, it would probably inspire you and help your progress.
Entering a bodybuilding show on the other hand (and this is all 2nd-hand as I've never done one myself) requires it to pretty much become your life for 2, 3, maybe even 4 months depending on how much fat you have to lose. You will have to starve yourself half to death, do specific contest prep and get a goofy spray tan.
Not to mention the fact that you have to learn how to pose an all that. Bodybuilding doesn't seem to be something where one can enter a competition on a lark.