We have a Voxcom home system. There have been a couple hiccups, such as a hardware malfunction, but overall have been pleased with them.
I called a few places and chose Voxcom based on services offered, company size, and responsiveness to alarms. Not the cheapest, but we feel their prices are fair. All of the companies I contacted had a three-year contract term, so it seems to be standard in the industry, as do automatic renewals, and penalties for terminating service prior to the end of the contract term.