I think N+2 updates are barely done pre release by users out there, so issues will rarely
be noted before final (F25 final in this case) lands. N+1 updates happen quite often
during N+1 alpha and beta phase, thus they'll probably see more testing and should be
recommended. OpenQA is fine, but it doesn't handle a comprehensive set of
installations to catch all the user-specific changes to installed packages or
configuration files.
If somebody wants a regular N+2 update cycle to have at most one update per year, he/she
probably shouldn't (and wouldn't) use Fedora but some more conservative distro
such as Debian.
So:
1) N+1 should be recommended
2) N+2 should not be discouraged