I had both, and now just have the 15 rmbp. In comparing the two, it really comes down to the graphic intense stuff you will be doing. I love the size of the 13", and I loved the machine for casual to almost medium level gaming because the 4000 graphics card is very decent. The screen is amazing as well. And for everyday stuff ie... surfing ect., it is great. But thats about where it stops. I create tech videos on youtube,(techsbookjunkie) and sometimes i want 2 videos running on the screen at the same time, one on me, and then the other on green screen or whatever. The 13 inch can't handle it. To me that's not to much to ask, but it makes both videos studder, very badly. At first I was like well I can do most editing on the 13" and then transfer to the 15", but this got old quick. Most of my editing is done on the couch, and the size is perfect. The 15" on the otherhand is a beast, I did get the 16gb of ram, but my goodness, I could probabally have 4 videos going at the same time, no joke. The combo of the quad processor, 16gb ram, and the 650 graphics make this machine very powerful. It is big, and it is heavy! Those are the down sides. Honestly, as soon as the Haswell comes on the 13" rmbp this summer, it will be bought Day 1! Great machine, just needs a little more power under the hood, and with Haswell hopefully going to almost double the graphics, the 13" will then be the perfect machine. Hope this helps. In other words if you can wait for Haswell, I think you should, but if not, and doing anything graphically intense, somewhat, go with the 15" max out ram.
