look at efficiency. It's not always neglible, was like 40% of my energy usage because I oversized the UPS. The efficiency is calculated from top power the UPS can supply. 96% efficient 3kW UPS eats 4% of 3kW, 120 watts, even if the load you connected is much smaller than 3kW
look at noise level. Mine was loud almost like a rack server, because of all the fans.
I replaced that noisy, power hungry beast with a small quiet 900W APC and I couldn't be happier