Most people on here will say go for the tone. I say go for the mid knob. I wish I could have both, but for my playing I prefer the mid control. In a mix, my fingers and the active treble can cover most of what the tone control would give me.
It depends what you like. I've found some GREAT sounds boosting either mid mids or low mids, I can get some more chewy Fender sounds or cool dub sounds.
Jarret, I know you don't feel you are missing anything, but I'll bet you would find a few more usable sounds with the mid control. It's a nice non-honky sounding mid that can actually reach down into the upper bass region.
The problems is that very few people have played two basses that have the same configuration except for this one control. For whatever it's worth, Moshe at the Hollywood store also felt the mid control was the way to go.
Whatever you do, please let Carvin know that you wish they would offer both options together. If they get enough votes, they may redesign the electronics for the next version so you don't have to choose.