Ridiculous debate. Kipchoge is winning everytime unless he bombs. Why? He is faster and would prepare himself better. Wanjiru was known to slack off in his preparation. If they knew they were racing each other, I can see Kipchoge being more ready to go. Although both have displayed incredible mental strength for the marathon.
Kipchoge's debut marathon was a minute faster than Wanjiru's. Kipchoge's PR is two minutes faster than Wanjiru's and Wanjiru couldn't hold the pace when he tried to go after world record pace. Heck, Wanjiru's best time is only 20 seconds better than Kipchoge's debut. In Chicago 2010, when Wanjiru had that great battle with Kebede, Kipchoge would have been a minute or two ahead after he dropped everyone at about mile 18 or 20.
Wanjiru's Beijing marathon was amazing, though, I'm not sure if anyone could have beat him on that day. But I think G. Mutai's 2:05.06 at New York in 2011 is just as impressive.
Wanjiru was a pioneer in career progression and style. He had the track PR's to compete for medals on the track, but went straight to the marathon at a young age. Since then, it's been a tsunami of young talented guys going straight to the roads and skipping the track altogether. This has a lot to do with where the money is at, but I think Wanjiru's example had something to do with it.