I haven't shot the SR9, but I have an m40 (not A-1). To me, the Steyr design is the best polymer frame pistol out there. I especially like its chassis design and its very sweet trigger (with short reset). Add to that: extremely low bore axis, full chamber support (standard rifling, not that this matters to me but it does to those who shoot lead), Tennifer finish, and it is built like a tank. Every once in a while, I will find additional things I like about it that I hadn't noticed before, such as a full metal skirt housing for the recoil rod base, which is fantastic if you wish to get a metal rod from BT.
Steyr jumped years ahead of all the others in my opinion and only recently have others started to catch up. None fully have though...they all have some shortcoming compared to the Steyr. Unless you want a different platform, I say get an S model Steyr to go with your M-A1.