I hate to be repetative with some of the others who posted- but I gotta go with Danielson, Kaval and Miz.
Danielson- well his talent speaks for itself- sure he is a small guy- but him, along with Kaval, have more talent in their little finger than most wrestlers in WWE and TNA, they can both keep up with the big guys. Since I mentioned Kaval along with Danielson I will just talk about them both here. Their mic work is ok, but it works for them. Danielson comes off as very humble- I pray to god they do not stick a stupid gimmick on him later. Kaval- his voice is just cool, lol- but its him. Both being small guys- they both take risk against bigger guys, but they are not predictable in the ring like smaller guys like Rey. Hate that they both had to go through NXT. As far as any other NXT guys that impressed me- Henning, Barrett, and Rotundo.
Miz- man has he come a long way- He use to be a joke in the ring- and out. Now, he kills on the mic- and has improved quite alot in the ring. He is a great heal.