Re: mera mera fruit
People also need to realize the Straw Hats have yet to come against a group of enemies that proved to be truly hard to beat, so its very unlikely we have even begun to see what the Staw Hats can currently do. First Arc was Fishman Island, and Luffy didnt even sweet when fighting Hody. Yes he was injured, but imo Luffy was just testing his abilities. First off, there were under water when he used some of his strongest attacks. Second, remember when Luffy was badly bitten by Luffy. Luffy commented that his haki shield was not strong enough to block attacks like that, which IMO means he could of dodged it (or that being underwater weakened him too much).
Also, look at how easy he handled the Punk Hazard arc villain Ceaser, besides that ONE time he under estimated his power and passed out from his ability, he quickly overcame the ability and kicked his butt very quickly.
I think once we start seeing flash backs to the Straw Hats training, reflecting on the difficulties they went through, we will truly start to be hitting an issue with people strengths.
TLDR: The person who is the weakest at the moment and have the little to contribute will get the fruit, and I think that Usopp.