The two biggest things to look for other than capacity:
- Line interactive versus standby. If you have a lot of over and under voltage events line-interactive is preferred. Standby will only kick in when power actually cuts.
- Pure sine wave. I think power supplies are better about this now, but for some time PC power supplies only really worked on pure sine wave UPSs.
I bought the CyberPower CP1500PFCLCD in 2015 and its been rock solid. I replaced the batteries for the first time last year.