You keep lumping the Oden and Roy injuries together. You say the Blazers hope is in a miraculous recovery. What if you got half of your wish? You can have Roy's knees whole or Greg's. Which would you choose?
Oh wow...talk about your stumper.
The arguments for Oden would be that he's a center, a completely unique talent, and his defense/rebounding abilities give you incredible freedom to mix the rest of the roster as you see fit. You don't have to surround him with particular players with the caveat that whomever plays with him needs to be able to score a little bit. On the other hand Oden hasn't produced huge numbers even when healthy, largely due to foul trouble and his raw game. We don't yet know what the finished product will be like. Plus the Blazers would be paying him a mint on top of what they're already shelling out.
Brandon has already proven he can lead this team to victory. He's an All-NBA player, the heart of this team when whole. You cannot argue with his production or his last-second miracles. He's already bought and paid for, adding no extra expense to retain. Shooting guards (and scorers in general) are more common than dominant centers, though.
It's a tough choice, made all the tougher because of my high opinion of Roy. But I think if forced to choose I'd take the chance and select Oden. Brandon might be able to give you something even if still hobbled. Oden's condition appears to be binary. He's either playing fully or in a coat and tie. You might get more added value by taking Greg and letting Roy add where he could than the reverse. Also I think LaMarcus Aldridge can replace some of Roy's missing scoring and star power. I don't see anyone replacing what Greg could do.
This is a question that needs to be thrown to the masses, though. You can have one healthy again: Oden or Roy. Which is your choice and why? Comment below.