Personally I like 13/5 the best.
Anyways, I have heard the 12 vs 14 stuff from electicians who sub for me and it is the same thing as the stuff I hear from plumbers who sub for me and run gas lines who want to go down to 1/2 inch pipe as fast as possible when I tell them I want it 3/4s. The same excuse is that 1/2 will be fine, which I answer "yeah for this application, but you dead end the homeowner from ever doing anything else. See that fireplace over there? One day he might want to turn it into gas and with this 3/4 instead of 1/2 line running by here all he has to do is tap into this line you are installing, instead of tearing it all out and running 3/4 later."
12/2 gives you more leaway for later, it should be cheaper too when you are running 3 12/2s instead of 5 14/2s. The difference in materials is always negligible, its the labor that kills you.