This is a fantastic question, and I honestly don't have a clue. The guy whom I thought would be good, Odom, has been somewhat of a disappointment. I think the best guy I can come up with at this point is probably Rudy Fernandez.
I completely forgot about Nate, mainly because he's been hurt here recently. AK isn't even a guy who had crossed my mind initially either, but now that you mention it, I can definitely see it.
jason terry easily so far. he's averaging over 20 a game coming off the bench. dj augustin deserves a mention as well.
I'd go with JT, thing is he's really a starter and we all know that. By the end of the year it could be Ginobili if they keep bringing him off the bench. A lot of teams seem to be purposely using very talented starters off the bench (Lakers, Jazz, Spurs, etc). Matt Barnes has been lighting it up as well. If he ends up coming off the bench in more games than he starts he would qualify as a 6th man.
They invented bringing your best player off the bench. Other teams aren't bringing their best player off the bench, but after Ben, the quality of 6th men in the league have increased a bunch.
jason tery fo sho. it should've been either ron artest or lamar odom but both of them aren't being as producive as they should, but now they're starting to come around. terrys getting 20pts, 4ast, 2 3pts, 1.3stl, 47fg%, but hes playing 35min. thats a cheap way to win 6th man of the year. rudy is more of a real 6th man. ballin the lights out in portland in his rookie season. 2 3pts, 10pts, 3rb, 2ast, 1stl, 90ft%, 41fg%, 1.4 tos, hes strait up ballin. could even be in the dunk contest. no dark skin on him so you gotta give him props.
Definably Jason Terry IMO. One of the dark horse candidates is Hakim Warrick though. He is averaging 11 a game, but has really been stepping it up the last five games averaging almost 19 points a game.