There are lots of factors that can play into this. What is your budget. Are you a casual developer, or is this your work machine. Are you going to be developing directly on it, or using remote or virtual machines for daily development.
Personally I use a Surface Pro 3, i5 with 8GB ram.
It runs Visual Studio 2015 better than most of my co-workers lenovos do. It's extremely portable, great for taking notes on, and when docked at my desk, gives me plenty of screen real estate to have all kinds of windows open. However when I am using it as a laptop, I use a different VS Profile to keep more of my windows/tabs/sections minimized until I need them.