If upgrade awards on international flights are important to you, it's probably OnePass' achilles heel. Other than that, OnePass is a great program.

There have been endless discussions about the international upgrade issue here but the long and short of it is that you can't confirm upgrades on international flights prior to 30 days in advance of departure, and in general they are very tightly controlled.

Regarding the difference between OnePass and WorkldPerks, they're pretty small.

I'd suggest a search on either of theses two topics for more information. They've both been discussed many times.