From the outside in, it's obviously safer to go with Vrabel.
Kraft has hired three coaches: Bill Parcells, Pete Carroll, and Bill Belichick. All three are likely going to the hall of fame. Bill Parcells was on the HOF track before Kraft hired him, Pete and Belichick were not. The Belichick hiring in particular was not highly thought of at the time, esp. considering Kraft had to give up a first rounder to get him. So I'll give Kraft some (but only some) latitude in assuming he's made a thoughtful choice if he goes with Mayo.
Perhaps even more important than the HC decision is the GM decision / coaching staff. Let's see how Kraft and their HC choice navigate what is going to be a huge organizational change moving on from Bill. They deserve our support as fans, and if things go south we will surely let our displeasure be known as well. It was always going to be tough to move on from Tom, Bill got 4 years to show things were headed in the right direction and he failed to do that. If Tom had 4 tough years in a row I think we would have all been ready to move on as well.