My truck is now 17 years old and has always had a US Auto alarm. They have never charged me a penny to adjust it, to help fix broken remotes, or any sort of service. The alarm has never failed or gotten stuck on, any of that sort of thing. They've been unfailingly courteous and helpful. Some of the bits are no longer made and they sort through boxes of old stuff to find things to make it work. My only cavil with these folks is that they're in Venice and I'm in Pasadena and it's a mighty long trip. But whenever possible and appropriate they've given the advice I need on the phone. They're the bee's knees.
Pros: friendly, cheap, easy parking, good quality, never a problem
Cons: too far away from my house