For that usage profile, I would go with the AMD model and save a few bucks, myself.
As for 14" versus 15": is your brother the type of user who will carry this thing everywhere, or will he tend to leave it on the desk pretty much continuously? If it will tend to be glued to the desk then you may as well go with the larger screen, because the extra weight doesn't matter. Otherwise, suggest getting the smaller, lighter unit as it will be easier to carry and more durable under the daily abuse associated with being toted around and folded repeatedly.
Abacus Model 2.5 | Quad-Row FX with 256 Cherry Red Slider Beads | Applewood Frame | Water Cooling by Brita Filtration