One thing to look out for is being able to disable the "power out alarm". Most of these start shrieking when the power goes out, which pretty much sucks at 2am. A surprising number of them dont allow you to disable the feature for home/home theater use.
One APC model said it did, and had a dip switch for the function, but still shrieked until I got at it with a soldering gun and removed the beepers.
I have a couple of cyberpowers I got at staples with a bunch of coupons for a decent price. They all let you turn off the alarm, and they also have an internal logging feature that lets you hook up a laptop and see all the outages, overvolts, undervolts, etc by the past week, month and so forth. Many others have good logging, but some require that the PC be connected to it and running all the time to give you a detailed historical log.
Aside from those details, one that supports an undervoltage condition is very helpful for some electronics that get a little 'sick' below 110v but dont necessarily crap out. My old series one tivo's used to do weird stuff if they saw anything under 90 volts, but wouldnt reboot until the power went well below that.