I had the same concern about balancing a 15 or 17 PB on my lap in my leather chair. The sides of my chair are large and I thought that the 17 would be a tight fit so I am sitting here typing on my new 15 and it balances quite fine. The 17 would also balance fine, but would be a tight fit albeit a larger screen. Either will be quite enjoyable. Make the decision based upon which you want to carry back and forth to work, etc.