I'm currently with rMBP 13 and I'm using it mainly for web development, as UI/UX stuff also.

The screen size is not an issue for designing; you can switch to more space, e.g. when designing I'm switching to 1680x900 and don't feel claustrophobic as on my previous MPB's 13".

I had high-resolution & anti-glare MBP 15", just before buying the retina, so I'm comparing it with the 13" rMBP and actually the retina feels more comfortable for designing stuff. Weird, heh?

I would max out the ram and SSD and go for the 13" model.

Thanks for the great advice. Eventually that's what I did, maxed out the RAM to 16GB and upgraded the SSD to 256GB and compromised on the 13" screen size. Apple Live Chat person said try this and see how you feel and if not then upgrade to 15" and I thought that kind of make sense. I hope I find 13" comfortable; otherwise I have to shell out another $500 for the 15" similar spec.

Are you going to be doing graphic/web design stuff yourself?

If Yes ----> Buy a 15" rMBP

If NO -----> Go to a store, look at a 13" laptop.

Is it too small?

If Yes ----> Buy a 15" rMBP

if NO ----> Buy a 13" rMBP

Yes, I do some design work as well and I used to live with a 13" MacBook hooked up to a 24" external monitor and it worked fine for me but wanted to get away from that monitor dependency.

The big benefit of a small monitor is that in the long term is forces you to be uber productive with the keyboard. You'll probably get more short term value from a 15" but more long term value from a 13". My keyboard mojo went through the roof when I switched from a 17" to a 13".

Something to consider: Xcode's UI, particularly for editing Interface Builder stuff, really benefits from a larger screen.

On a smaller screen (13" or 11"), you'll find yourself constantly toggling panels on/off so that you can see what you're working on.

I clearly get what you meant, been there and toggled panels enough to get away with it. I'm counting on the retina display and higher resolution to get around a portion of this overhead.

For web development a MacBook Air will do just fine, even with 4 GB RAM. Screen size shouldn't matter, you're probably going to hook the laptop up to an external monitor anyway.

for development, i think they're all the same. I prefer the 13" because its more portable, or the Air for better battery life

For design, the 15" would be nice