When I went through formal rush, I didn't consider the national orgs nearly as much as the specific chapters. I knew that for the next 4 years, my collegiate chapter would be my closest connection to whatever sorority I decided to join - and beyond that, I would have to see where life took me.
I dropped out of formal rush to join a local - again with the mindset that it would be my home for the next 4 years, and then I'd see. Happily, we became a chapter of AEPhi, and happily, I settled in the Northeast, where AEPhi is strong.
That said, I wish I'd done more research into the sororities at my school before going into rush. I might have ended up somewhere very different... naaaah, AEPhi is where I belong.