for my work flow I would definitely prefer 13 over 15.
Here are the Macs I have used over the years:
- 2007 Macbook Pro 15
- 2011 Macbook Air 13 (Sandy Bridge i5 4GB RAM)
- 2016 Macbook Pro 13 TB (16GB RAM)
Most of the time I use my laptop while I am travelling so I value portability over power. That said for what I use it for, I don't really see much value with a 15 inch screen with quad core. (to me, if you have to ask whether you need a quad core chances is you probably don't and you will know it if you really need it)
I usually use my laptop for web browsing, email, music, programming (xcode for iOS, VM in Linux and also Windows for Visual Studio for .net)
My Macbook air with 4GB ram was a bit restrcting since It would be a lot easier for me to be able to run 2VM at the same time but since upgrading to the 2016 mbp I haven't once wish it was quicker.
That being said I do have a desktop computer both at my office and home (both windows machine) for me to use (I usually do use my desktop when I can, but I think I will be happy to use my 2016 13 MBP if I do not have a desktop to use)