I prefer the 15". As I'm getting older my eyes seem to prefer a much larger screen. Also prefer the extra power and dedicated graphics card when I need it.
Carrying it around hasn't been a problem. A good backpack will make that a non issue. But I've carried my late 2013 15" MBP in messenger bags with no issue. Though getting older, my shoulders prefer a backpack now a days.
On planes and tight spaces I usually just use my iPad. But when I needed to get work done, I've sat in economy seats with my MBP. It was tight, and a bit uncomfortable but it just made me swear I get work done before the flight 🙂