I think it'd be best to spear either a)upper keys - Islamorad/Key Largo for instance, b)Eliot Key, or c) a bit past Fowey Rocks.......all are good spots, easily accessible, and have good vis.......as for the prize, I'd say the heaviest fish should win.....simple that way......no limit other than bag, so that those who don't win don't aren't also a little down that they didn't spear as many as they could have.....in terms of actually awarding the prize, If I were gonna coordinate it - why not take a poll of all contestants' preferences.

That is, give them a choice: mask, suit, gun etc........provided the entry fees cover cost whichever choice comes up most is 1st prize, next to most 2nd etc......also a couple of DB shirts as consolations.....maybe also, prohibit Scuba, or have a separate tourney on the same day......
cheers,
CBeast