I use pro diem. The advantage is that they determine whether to use the standard per-diem rate, or the city-specific rate. You have to choose to use one or the other for the entire year. Which one is right for you depends on where you fly and how often.

If you're a long-hauler, and stay in Tokyo, HKG, Narita, etc use city-specific.

If you fly a 1900 into small trailer-park meccas in the south and midwest, use the standard rate.

Anything between those extremes, and you need to calculate it out to see which option provides the best return.