It's not worth the premium to fly up front domestically. The first class seats are not lie-flat, the food service isn't comprehensive as international flights, and finally the flights are short. Hence, the fatigue factor is about the same as flying in Y.

Thus, I'd rather fly LCC's like WN, B6, or VX, be treated well, and save some money. (Of course, if the price differential between Y and F were much smaller, I'd just fly F.)

International trips > 5 hours are a different issue.