While a tricky question, I think that its worth noticing a couple things:
1 - Rupp's half marathon PR isn't in the same ballpark (sub 60) as Hall's, in fact, Rupp's is slower than Ritz's at 60:00 flat. Ritz has run 2:07 under totally ideal conditions. Rupp hasn't broken into 2:08 yet.
2. - Everyone is foreggtting that Hall was on 2:06 pace in London, and asked the pacemakers to go FASTER. And he was on 2:06 pace for part of the 2007 Trials race on the central park course, and then had no reason to keep running that fast.
2007 hall versus 2017 Rupp? Hall wins. Hall was the greatest American-born Marathoner that we've ever seen. His times show it. Rupp is a great, competitive Marathoner, and he has the hardware in certain races, but Hall was not at his peak in '08 Olympics, knew he overtrained, and still ran 10th in the craziest Olympic marathon of all time. Hall was a marathoner in the mold of the Kenyans, and while Rupps final 10K in Chicago was impressive, without him going to Berlin or London, we're not seeing what sort of speed he really has. I want to see him at 22 miles in London with the lead pack at 2:06 pace before I believe that he could have beat the 2007 Hall.