You will probably get a lot of different opinions. My own opinion, and the reason I gave up trying to carry a 15", is that it just doesn't fit into the bags I travel with. It's a square inches, not cubic inches, not weight, problem. YMMV, though. For me, a 13" is a lot more portable even though you give up a lot of screen real estate. My personal conclusion was that if I was using a portable computer, I was ok giving up near-desktop screen real estate. It's all about the trade-offs...
yah if you use a couple different apps at a time, take some tape on your monitor, that won't leave any marks, and square off 13 inches and the diameter, and see what it looks like. LOL. also going to the apple bar you can test as well.
i had the 17 because i use it for work showing documentation to others, and when that died, i ended up with a 15 which is much more difficult for showing others things. however, its quite portable. I'm not sure I could function with less than 15, but it really depends on you and what apps you are using.
i live in a rural area, and i have to drive, as there is no public transportation. or should I say we recently got public transportation and it goes certain places one pick up in the mornings.
matte on the screen helps as the sun will catch you in the most annoying times. the 15's I'm not sure if they are anything like the 13's. But for the 15, you'll need a little adapter, as the charger pops off if you sneeze. http://www.newertech.com/products/snuglet.php
its my way of working on long road hours and its a good work horse. Which is why I prefer it over the iPad, I can do more with it. i go back and forth with computing vs. portability. the iPad was the better portability, and i had a strap and just had it, and a small wallet and did well for a long time, and left the laptop as a hard drive with monitor in clamshell. and would take it for heavier appointments lets say. the iPad, you can have in the grocery store, vs opening your laptop, but you can do all that with the phone.
the 17 was like 10 lbs. So this one is so light, its as light as my ipad2 was. I can only imagine that the 13 would be even lighter. and then the air better than that.
what are your main chores, that you want to do when you are on it? because that's the real test, is getting the one that is compatible with what you need to do.
How portable is the 15 inch rmbp? Does anyone travel with it a lot and use it in coffee shops, trains and planes?
I travel on business all the time and it's really portable.
I find the 13" too small. The 15" is just nice.
That said, I always travel business class or on a corporate jet, so airline tables are much larger and large enough to comfortably accommodate my 15".
In trains and coffee shops, it's quite portable too. In fact, I find the 13" can have the risk of slipping off my lap through the gap between my legs. The 15" prevents that.
Besides, I need the dGPU on the 15".
My small, lightweight 13" rMBP works well for me as a portable machine, although without the iMac I would have stuck with my 15" rMBP for the larger screen and quad-core CPU. However, I don't travel much.
Makes me wonder why you even have the 13".
Can you still run 2 apps comfortably side by side on a 13 inch?
Its portable, and the weight difference between the 13" and 15" are such that I don't think the extra weight and size is will negatively impact the 15" rMBP. I have traveled with both and they're about the same imo.