I like an all around larger tooth count. I ride 77" but on 47/16. It makes it harder to throw a chain. But between the two quoted, it's not such a big deal. It's about a 6% difference between the two.

(BTW, by Sheldon's calcs, 42/15 is 73.6" or 75.6" depending on whether you're on 700c or 27" wheels. http://www.sheldonbrown.com/gears/)