I don't think I know enough about the TNA guys to comment on them (I have never watched an episode of TNA from start to finish ever), so i'll just comment on what I know, the WWE guys
Evan Bourne, Goldust, Primo, R-Truth Santino, Vladmir Kozlov, William Regal, Yoshi Tatsu, Zack Ryder
Bourne is a future main eventer for sure, as is Ryder and hopefully Truth. They along with Tatsu, Primo and Santino should be in contention for US title right now. Kozlov should be a main event heel (What happened to the days of him feuding with Taker?!). I understand Regal and Goldust are veterans now, but they should be in the US title picture really, even if it's to put others over!!
John Cena,...that's about it lol
The Dudebusters (Croft and Barreta), Chavo Guerrero, Chris Masters, Christian, JTG, Matt Hardy, MVP,
Not sure if there is anyone over-rated on the Smackdown roster. I don't think Rey Mysterio is over-rated, it's a bit annoying to see Undertaker go straight to the main event every-time he comes back but where else would you put him?!
I will say though, the under-rated guys on Smackdown are overall more talented than the under-rated guys on Raw. MVP, Christian, Masters, and Hardy (if he gets back in shape), and indeed Chavo are talented enough to be in the main event. The Dudebusters are talented enough to be tag champs.