Really looking forward to this. Hopefully this main events, and I expect a rabid crowd atmosphere (something similar to Wyatt VS Shield on pay per view).
Tricky to pick a winner for this, but I'm going with Evolution. Yeah, Triple H, Batista, and Orton are decorated world champions and future Hall Of Famers, so you could say they don't need the win, but Evolution doesn't need a 100% clean win.
Triple H could sneak a sledgehammer in here somewhere, or maybe Orton and Batista pull a dirty trick behind the ref's back to help Evolution pick up the win. And you preserve The Shield's momentum, because Evolution couldn't win without cheating.
Also, I agree with The Eighties about Evolution's reformation. I really don't see the point in a big reunion, if the plan is for a one night only match and a loss. Evolution should stick around for a little while, with Triple H abusing his power to torment The Shield, and maybe they'll tease a fourth member, or someone to fill Triple H's spot as an active full time wrestler.
And I don't see a Roman Reigns heel turn happening. They're still in the early stages of a face run, and Reigns is the stand out star of the group, so you're crippling The Shield if you take away Reigns.