I only drive on the street so I went with the inboard brakes. If I were to build my car again, the only thing I would do differently is to go with the outboard brakes.
While it is true that you can remove the access panel to get at the inboard brakes, I find that removing the seats to get to the panel, and then reinstalling the seats when I'm done, takes longer than actually doing whatever type of servicing that I wanted to do to the brakes or rear in the first place. I know some people claim to be able to remove the access panel without removing the seats, but that hasn't worked for me- can't get my hands and a screwdriver back there with the seats in. It would be so much easier to just jack the car up, pop off a wheel and have full access to the brakes in 5 minutes.
The extra cost of the outboard brakes is not that much more than the std rear if you do it now, but if you want to retrofit it later on, it will cost you almost as much as it would have if you would have purchased the outboard brakes initially- I've asked about it.
So I would go with the outboard brakes now because you cannot easily (or inexpensively) upgrade that later on and forego some other options now which you can more easily upgrade letter on when the budget allows.
Plus, the outboard rear is so damn pretty to look at
