I'd lean towards Louis, although a Liston win is a real possibility. Brutal war, but I see those beautiful, compact Louis combos taking their toll on Liston and taking him out late.
It would be a lovely fight. Liston will hurt Louis, and badly. But Louis, in his prime, knew how to shake it off and come back. I'm not so sure Liston could shake off Louis' punches. Sill Liston was bigger and stronger...so it's a fight I wouldn't bet on either way. If I had to pick, it'll be Louis, nervously.
Liston wins first fight, Louis wins rematch and any bout that came after that. Louis could make adjustments, Liston could not.