HW: In the UFC? Probably Schaub, but that's not saying much. I think he's a fringe top 10 guy at best. In MMA as a whole, Konrad has top 5 potential with his elite wrestling and smothering top game.
LHW: Phil Davis by a long mile. He's already beaten the 3rd best prospect quickly in Alexander Gustaffson. He's almost a sure-thing top 3 title contender down the road. The only guy that comes close to him is Roger Gracie, but there are questions about his committment and his ability to take the fight down to the ground.
MW: Very weak division for prospects. The best in the UFC is probably Brad Tavares, and I'm not even sure he's a long term UFC fighter to be honest. I think if he puts everything together he can be in the 7-10 range of the weak MW division. Overall, Chris Weidman is clearly the best prospect. A near can't miss. I think he's one of the most sure-fire future champions in the sport simply because of the division he fights in.
WW: Rory McDonald is the best WW prospect in the world right now. To think, that this guy as pretty much a kid was probably 10 seconds away from being a Carlos Condit who could be challenging for the title in the near future is astounding. Slick ground game, good chin, cardio, and respectable stand-up and wrestling skills give this youngster top 3 potential at the weight.
LW: Narrowly eeking out Mr.Barbosa is Charles Oliveira. Guy is a fearless striker and a slick, lightning quick ground game that can only get better as he ages. At only 20, this guy will improve by leaps and bounds and as all the physical tools, including lighting speed and agility and a neverending gas tank(a quite hyperactive one at that) to be a future champion, possibly a dominant one.
FW: Tough, tough, tough, but have to go with Chad Mendes. He's so inexperienced but beating all the top guys in the WEC/UFC with simply his stupifying top control and improving striking. He's a top 3 guy in the near future, but I don't think he gets by Jose Aldo.
BW: This is pretty clearly Michael McDonald. This guy is SUPER impressive, and like Oliveira and his fellow McDonald, Rory, he's still a baby in age terms. However, mentally, this guy is a 30 year old contender in his prime. He's THAT confident, THAT mean, and THAT cerebral. He'll take your punches, knock you out, or sub you, but at any rate you are going to get finished, and Michael prefers it quickly.
This guy is a sure-fire thing to fight for a title one day.