Go for a bigger screen if you surf the Internet or work with large documents.
If you can afford it, go for a bigger screen anyway.
I use two notebook PCs, one 14", the other 15", the bigger screen feels much more comfortable to work on viewing wise.
Surface Pro (2017) vs Surface Pro 4
20 groundbreaking 3D animation technologies coming to Siggraph 2017
iPad Pro 12.9 vs Surface Pro 5
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.