There is ambiguity as to wheter "main" means only.
If I got the MB it would be used as my portable Office and casual device with a 15" rMBP at home. My usage would likely be 70% MacBook, 30% MacBook Pro. In that sense it is my "main" machine.
If I had to pick one for my only machine it would be without a doubt a MacBook Pro. I used my 15" MacBook Pro with 16GB of RAM as my workhorse with my LR photo library, VMs, and videos. I can't give that up, but I'm using an iPad with a keyboard as my in between iPhone and MacBook Pro device for school and casual use. This MB would fit nicely there.