It all depends on the guitar, what you like yours to sound like and how and what you play.
As an example, on the AGF there was a fellow inquiring about Maple Taylor 214ceDLX maple. I listened to the recordings of that model and realized that the bass on those guitars had little projection and the brighter were...well, bright. 13's would probably have done that guitar a lot of good, increasing bass presence and tamping down the excessive brightness.
I've tried lots of combinations on my 614 and 814 and always look for balance and the right sound. On my 814 I found that both 12's and 13's provided a good balance, but I (at this moment) like the zing of the 12's, even though the 13's provide more projection.
The best way to know is to test for yourself.