It depends on your project's timeline and sensitivity to working with milestone and/or release candidate releases.
If you require a stable release, 1.0.x should be your choice. But if you're willing to work on the latest and greatest stuff, you can start working with 1.1.0.BUILD-SNAPSHOT now and follow the work through milestone and RC releases until the final GA release.
I can't speak with certainty to when the final GA release will be, although I would anticipate it in the next couple of months. But I plan to release 1.1.0.M1 in the very near future. I was hoping to cut the 1.1.0.M1 release tomorrow, but I've still got a few loose ends to tie up, so now I'm shooting for Nov 26th (again, no promises are being made here).
Spring Social Project Lead