which version to use?

when browsing the download section i see quite a few versions within 5.x (from .0 till .8) with quite a difference in latest release, some from 2017 and even some newer ones from 2016. the release notes section at the download only mentions 5.3, 5.5 and 5.8.

is that similar to fortigate with 5.2.x (stable, for older units), 5.4.x (current stable) and now 5.6.x (latest)

is there any advice or personal experience on which to take or stay away from?