Agree with the Marin, but if for no other reason than it has puncture-resistant tires, which are useful.
I disagree with the above comment about flat bars and long rides. Though a singular hand position certainly has the potential to cause discomfort over long rides... 1) 6 miles 1-way is probably not long enough to do you any harm at all, 2) 'fit' makes a bigger difference than multiple hand position options, 3) you can have just the same pain or nerve compression problems with multiple positions.
Also it looks like that Marin has mounts for a front low rider rack. While I doubt you'd ever use that from how you describe yourself, I think it's a thoughtful bit of design on Marin's part, and cool to have the option.