This question might seem a little ambiguous; I'm looking for a good Star Alliance FF program to join. The obvious answer probably is "pick the FF program for the airline you fly the most" but that might not be the case for me...

I actually rarely fly the SA carriers. Skyteam just has better times to my destinations, so I tend to fly them more. In the near future, however, I will be flying US, SQ and LH.

Of the carriers, I have flown US Air the most (which isn't saying much) and they have the most Star Alliance routes to my home city, but I sort of consider them a "loser airline" with few destinations and routes overall, especially when compared with the other star carriers. Being an American, should I join US or UA? Should I join another international FF program?

Thanks!