As mentioned above, this question is hard to answer without knowing more details. Essentially, it is up to personal preference. We have individuals on our team that swear by different-size screens for many reasons. This also can change based on whether you use an external monitor as your main display. The portable route would be to pick up something with an 11 - 14 inch display. This keeps the device maneuverable on a train, in a coffee shop, or on the go while still giving enough screen real estate to get work done. A 15-inch screen or larger becomes quite cumbersome, but at the same time, it grants significantly more space to see your work.