+1 I just purchased the 13", 8GB, 2.4 GHz, 256GB SSD version to replace my aging (late 2006) 17" MBP. This model makes the older top of the line MBP seem like a slow dinosaur. I already have an i7 quad core iMac so this was bought for true "laptop" use and it's light weight is ideal for traveling or surfing at a local Starbucks or anywhere with free WiFi. It's really fast and the retina display is awesome.Honestly it depends on your needs. I chose the 13 because if I want the real estate I have a 27" iMac. I picked the 13 for portability. I never even looked at the specs of the 15" models. If however size matters then what made me make my choice won't work for you.
So it really boils down to size versus power. The 15s are more powerful, but the 13s are more portable.
Hope this helps.
13" rMBP: 31.4 x 21.9 = 687.66cm^2I think it's funny that people state the 15" isn't as portable as the 13". That's ridiculous. The weight and size differences are minuscule. You can take the 15" everywhere you can take the 13".
The 15" will always be better in every aspect.