I'll bet that when you walk into the studio, that choice will be made after a lot of thought, and a lot of trying stuff out. And it will be very particular. And the particular guitar/amp will matter.
What say you?
That's actually a trenchant question, since I'm finally getting my studio floor redone tomorrow so I can set everything back up.
The answer is yes... ...and no. It varies. Sometimes I have a pretty clear idea of what I want in a part, and the choice of guitar/amp/whatever is obvious. Sometimes there are a couplefew options that might work, so I try 'em both/all and see what sticks to the wall best. Other times I have no bloody idea, so I just grab something and have at it then try something else then try something else... That's not very time-efficient, but in my case time-efficiency is not usually a priority. If it were, I'd do what you do and limit my choices. For example, if I were to go into an actual studio to record my next CD (which has been discussed and even planned, but it has yet to actually happen) I'd probably only bring three guitars and a couple of small amps. Amp-wise, I know the studio would have other options, and guitar-wise, well, I can always do overdubs later...