1.8 has been postponed. (EDIT: as @Stefan explained two posts later the update is still available, but users don’t automatically get a notification to install it anymore)
1.7 was only pre-installed on some devices
1.6 should work though.
or you could apply for the beta-testing program for 1.8.2. it’s working quite well. most problems occurr when (re)installing google services, but i guess that was problematic in every version (i don’t know, i never did it).