I currently use ADT and it's kind of like breathing. You don't realize it's there until you focus on it. I haven't had any security problems since purchasing a package so the ADT sticker must at least be a deterrent. Otherwise, ADT doesn't really have that much of a presence - no service checkups or updates.
The salesman who introduced us to vivint was great - low pressure, very informative, and very professional. The security system alarm was fairly easy to use, though we never had an incident where it was tested for a break-in or anything. Ultimately we stopped the service because we could no longer afford it.
There have been a few break-ins in my area recently and it made my whole family worried, but ever since installing FrontPoint my family has no longer worries about security. Setup was very easy and the phone app is well designed and simple to use. I would recommend FrontPoint to everyone I know.