I've redeemed all of my United miles for an upcoming flights for my family and am now at zero. I am thinking of switching to US Airways DM since my primary is the Starwood AMEX which transfers 1:1 at US Airways but 2:1 to United MP. However, it seems there is more availability/flexibility in booking award flights on United than US Airways in my market (SAN).

My questions is if I switch to US Airways DM, will I be more limited in booking Star Award flights on United than if I had United miles? Are United and US Airways equal when it comes to booking other Star Awards (on other Star Alliance flights --- like Thai, Singapore, etc.)?

Thanks in advance!