I know this has been covered a lot. I think I know all the arguments. I used to comute on a 26" montain bike with slicks, as good as it is, I don't think it ever rolled half as well as my touring bike, with 37mm tires even.
I am contemplating building a custom frame, since I don't fit perfectly off the rack. I am struck with how many tire choices there are for 26" wheels, even for touring. They weigh less, spares are easier to pack. I have some very racy Bontrager rims 36H for 26" a custom deal back in the early days of MTBs, never used. I like the fact one can get gear lower on a 26" frame, I like the extra space for bottles.
I was contemplating making a 26" rear vs 700c front, but the tire spare requirements are holding me back. The lower 26" gearing is right up my alley.
My only reservations are rolling resistance and the rougher ride. I saw some Panaracer kevlar armoured tires 26'x1.25, and they look just right, but would they roll with proper inflation, and would they shake my teeth out pound for pound of pressure versus the 700C?