Stable system version recommendation

I would say it depends on what features you need for the deployment. But in general I'd say that version 13.1.1.4 is a stable version to upgrade to.

It's a Long-Term Stability Release with the latest Maintenance Release. So it contains many of the newer and expected features with only bug fixes applied.

I personally believe that it's still a bit early to upgrade to 14.x because I have seen some weird problems in a customer's lab environment who jumped to 14.1.0.2.

But I guess I'm a bit of a chicken when it comes to upgrading to newer versions. :P

I hope this helps!