Originally Posted by NickB
If you are likely to fly around the 25K-30K mark, there is not much to distinguish between the programmes. I'd go for one of the North American ones for domestic upgrades.
OK offers its silvers systemwide free (for long-haul they charge 2k miles each way) upgrades. However I wouldn't really expect them to actually offer priority boarding, even on their northamerican routes.
Originally Posted by NickB
One thing to note is that AZ and OK will give you access to their own lounges at the first rung of the ladder (for OK, this means PRG only.).
That's what is stated officially, but I've been able to access other lounges with my silver card (the first time it happened to me I thought it was the agent's mistake, but it wasn't) ^
Word of warning re KL's FFP: it will be merged into F+ sometime sooner or later and PE status is threatened with extinction.