MacBook Pro Retina 13'' vs 15''

Hi! (First of all, I would like you to excuse my english, it's not my native language) I'm looking for a MacBook Pro Retina i7. My big question is: 13 inch or 15 inch???

Now, in view of I need to carry out it, and I need the battery life to be long enough, I would bought 13''.

However, 15'' inch MacBook, despite not being "so" portable, has a Quad-Core processor, which is essencial...

To sum up, I will tell you what am I using of this computer: my main interest is to design some games and programs, and some benefits of PC's. (I use VMWare, and I like it to be fast and effective). I'm a musician by hobby and I love recording some songs on Garage Band, I usually use it. I also like editing some photos and sometimes (not too often) videos.

This is what I would "do" with my Mac, additionally to basic things just like navigation, iWork, and some little games. I would like you to recommend me which of them would be better for me.

Thank you very much for your advice and excuse my english again.