The 13-15-17 choice is simple. Get a 13 if you are planning on using it on a daily commute. The 15 and 17 are too big for train use really, they get in other people's way. Get a 15 if you need a bit more power and you are using at at college/work every day but not so much on a commute. Get the 17 if you mostly keep it at home but like to go room to room to avoid becoming a hermit and stay sociable, plus get the big screen for proper application work and also the better audio due to larger speakers. The sound is pretty decent for a laptop. It's not miraculous or anything, and I find myself plugging in the amp when I'm near it, but having it as your first option for music is no problem. The 17 has the advantage of the extra connects as well. If you like to work in a two screen situation, then the 17 is still a good bet - you can have Final Cut on the laptop and the output display on the external. I find editing on a 15 or less a bit too restrictive.