I would say Emmanuel was more impressive. The reason being there was no tail wind so his last 10k was his pure stamina and endurance over others.
If I look at Boston, we see a number of top guys running incredibly. I know these are good runners, but Ryan Hall's training does not put him in 2:04 zone if not for the wind. We know Geoffrey Mutai is a 2:04 - 05 zone athlete, so his 2:03 is just what I could have expected given that Ryan could also get carried to 2:04.
As for Emmanuel Mutai, this guy was not considered for a win, let alone a course record. That means his results are a great improvement and quite incredible.