I second the recommendations of being able to turn them on without AC power, and DEFINITELY the ability to silence the alarm. If you may be running unattended equipment, make sure the equipment and the UPS can communicate with each other so that servers and the like may enjoy an orderly shutdown. Never, ever, plug anything into a UPS that has a high transient load, including anything with a motor (including all species of pumps and compressors) laser printers and floor buffers. Yes, the cleaning crew at a former employer took out a UPS and killed the server it was protecting by plugging in a floor buffer. My suggestion is to put child proofing electrical outlet plug covers in each unused outlet, and follow that up with a sign reminding people that you will commit unspeakable acts upon their bodies if they so much as look at your UPS crosseyed.

Runtime degrades as batteries age. Budget to replace your battery or batteries no less often than every five years. If you need to have 90 minutes of runtime, buy at least 50% more (135 minutes) with 100% more being better.

The only brands I would consider for myself are APC and TrippLite. My experience with their consumer grade gear is limited but positive.

Disclosure: I've sold both brands before, however my current employer sells neither.