I went through this same decision process a year ago as the OP and decided on a 13" Mac Pro (Late 2013 model w/retina) with the 2.8 Ghz i7, 16 GB ram, 500 GB SSD. I also attached the Thunderbolt display for my office desktop with an Apple Trackpad instead of a mouse.

As I write this, Activity Monitor says I am using 9.06 GB of RAM running Safari (streaming Bloomberg audio and FT), Outlook, PowerPoint and Messages. When I run on battery I typically get well over the stated 9 hours of life on wi-fi. The main reasons I got the MBP instead of the MBA was the retina display (yes, you can notice a difference side-by-side), the HDMI port and the SD card slot. Also, the ability to load it up with 16GB of ram, although I am not sure if the present model of the MBA can now support it.

At the time, the MBP was only a 1/2 pound heavier than the MBA. Now, I think the difference is a bit less. Compared to my old T43 TP I didn't mind the additional 1/2 pound. I tend to keep PCs for a while so I a glad I opted for the MBP. A very nice machine.