Best move is for OKC to suck it up and extend him. Or, let him hit RFA and just match. Fine.
If they really want to trade him, the move is probably to Utah for either Favors or Kantor, straight up. For Utah, this un-gluts their PF/C spot and gives them their best 2 guard in...ages. Really rounds out their lineup. If Harden agrees to an extension as part of the trade, then Utah also gets a great player locked up in a place that has a hard time attracting FAs and had to send D-Will away because he wouldn't stay as a FA and they didn't want him to leave for nothing.
For OKC, with Favors they get 1 more cheap year and get a real defensive big; with Kantor they get 3 cheap years to avoid the tax. They start Sefalosha, and look to fill in SG with a sniper from the scrap pile.