I think most people would prefer the 13" due to form factor, however there is a lot to be said about typing comfort on the 15" (it is far more enjoyable thanks to a rest area for your wrists, while on the 13" it can dig into your wrists). If you are just browsing/watching while it's on your lap, the typing experience may not matter as much, but if you are looking to type a lot on your lap, I think the 15" is a good shout.