First off, I think this really depends on what happens during the off season, and we can probably tell what the FO's opinion is by what moves they make (If they sign 2 or more small forwards, they probably aren't planning on G-Time starting at small forward, if they sign a good shooting guard, they might either be expecting him to play Small Forward, or switch around between the two).
My personal opinion though, is that he should play Small Forward, with a little bit of shooting guard, and (until we get our PG of the future) I also think he could and should be playing "Point Forward" more often as his ball handling skills develop. Reasons for these after the jump.
The three main reasons Gordon should play Small Forward are:
1) We already have a good Shooting guard that could possibly start next year in Burkes.
2) If I remember correctly (correct me if I'm wrong) Gordon has a better PER at SF.
3) It seems so far like the FO thinks that Gordon is a SF.
I really like the possibility of the starting lineup of Devin, Borkes, Hayward, Favors, and Jefferson, and depending on matchups, we could also start Devin, Hayward, Millsap, Favors, and Jefferson. This is only if a move isn't made to move Millsap (as much as I love the guy, if he becomes the next in the line of Earl, Raja or CJ and complains about minutes, i swear!). If Sap is fine with the role and extra minutes at the SF spot, I don't see much happening to our roster other than trying to get rid of Raja, probably picking up the options on Tinsley and Carroll, trying to re-sign Evans.
As Gordon bulks up a little more and becomes just a little bit more explosive, I think he could have a break-out year, regardless of position. I think we should prepare for the future and let Burkes start as well, which means Gordon would be at the SF position.
Next year is going to be fun!