Consider 13.7 as the fully tested and rock solid version that's recommended and completely supported - having said that, customers are using 14, 15, 16 & 17 successfully without any issues.
I think the bottom line is that 13.7 is considered the minimum viable version and thus the one that we have historically recommended, but there's no significant reason not to upgrade. Some of our newer deployment templates suggest 16.8, for example.