Goldberg never won the WWE title.
I'm going with Big Show because that was who he had one of his last two feuds with was Angle. He has held the WWE title and WCW title and has been away from WWE long enough to not have to worry about contracts, no wrestle clause and all that nonsense.
Correction, Goldberg DID win "a" W.W.E. Title. He may not have won the W.W.E. Championship (currently being held on Raw) but he was the World Champion (at the time, on Raw) & therefore, a Heavyweight Champion in the company, which was what was stated.
IF, you claim that to not be a "Heavyweight Championship" then you must take Booker T. out of the assumption for being Sting's partner, as he was never the "W.W.E. Champion," either.
I will remain solid with saying it'll be Booker T, or Big Show. My reasons for each are as follows.
Booker T.: He's the freshest, free agent. And he wants to continue in the business without a heavy schedule. I think T.N.A. would be a great fit for Booker T, as long as he doesn't pull a Rikishi & end up fired 3 weeks after being brought in.
Big Show: Somewhere I've been reading that people are saying whomever the mystery partner is, its someone who has "heat" with Kurt Angle. Well, while I don't think they have real life heat.. Big Show fits the qualifications. He's been a W.C.W., W.W.F., W.W.E., & E.C.W. Champion. If anything, he's been a World Champion in every company he's been with, including E.C.W. (if you wish to count it as W.W.E. owned)
Now, regarding the heat. Show & Angle had several feuds, but the backstage one that sticks out is.. Angle was set to be in Big Show's position, when Angle requested his release from the company. Therefore, Big Show was the unofficial back-up that had to run with the ball, when Angle refused to stay & do it himself. Perhaps Show will hold a bitterness (for some odd reason) for that?