The older 5500 models (5510, 20 etc.) cannot go past 9.1(x). 9.1(7.16) is the latest and is recommended as long as they have the necessary memory upgrades to go beyond 8.2.
https://software.cisco.com/download/release.html?mdfid=279916878&flowid=4374&softwareid=280775065&release=9.1.7%20Interim&relind=AVAILABLE&rellifecycle=&reltype=latest
Other than that, we advise our customers to run the Cisco-recommended version for their platforms (unless they require a specific feature that is only avialable on a newer release). Right now that release is ASA 9.4(4.5) - it has a "gold star" on the Cisco download page.
https://software.cisco.com/download/release.html?mdfid=284143129&flowid=31543&softwareid=280775065&release=9.4.4%20Interim&relind=AVAILABLE&rellifecycle=&reltype=latest
Most of the "certification" our customers are interested in is passing a third party audit (often for PCI/DSS but also for other legal or regulatory reasons). That's as much (or more) configuration standards than it is what software version they are running.