I like all of them, but Ambrose has always been my favourite. His character has so many facets to it, he can do or be anything. I like his style in the ring, and his mic skills are fantastic. Even with all his losses he's still getting a lot of TV time and a good pop from the crowd.
Everyone says Reigns got the huge push and he did, but Rollins has turned into HHH's golden boy. Rollins is another one who is great in the ring, face or heel, mic skills are gold, and he's just such a cocky bastard. He's the perfect heel, never satisfied with what he has, always wants more, and pisses everyone off to get it.
Reigns needed the most work, and in a way still does. Yes he had a hell of a match at Mania, but again he's still getting mixed reactions from the crowd. He has the longest way to go, and that's down to his inexperience. He has the best look out of the three, but that will only get you so far. Once he gets more comfortable in the ring and on the mic, he'll look a lot better. Maybe add a couple of moves, we all know he has them, just watch his NXT matches, he could surpass the other two. Unfortunately he's a little damaged right now because of the Rumble fiasco, but I think he can recover and over time he'll be fine.
So all in all, the three of them are off to nice starts, and if Vince doesn't fuck up again, they should be the future of the WWE.