12inch or 15inch?

I have a 12" PB and I don't really mind the size. The thing that I do to offset it when using it at home is to disconnect my 17" monitor from my PC (I'm a recent converter) and hook it to my PB and span the screen. That offsets the screen size for desktop use and development, but on the road I like to have the smaller size, which means smaller bag and everything, too.