ADT has gotten far too big for their britches, when it comes to cost. Hoping someone out there has made the switch.
I have SimpliSafe. For like $200 up front and $10-20/mo I get full home security.
Pros: super, duper easy set-up; reliability has been good on sensors and connectivity; the interoperability between devices(phone app, keychain dongle) has been good. The responsiveness has been good when alarms are triggered. The varying solutions and ability to build your own security situation ad-hoc is pretty simple. Decide what solution you want for each area: entry sensor, motion detector, etc, and then just install in 2 minutes for each one.
Cons: The video situation is sub-par. I think now they have video solutions, but it doesn't look too integrated. I haven't waded into this water, as I use a separate Nest-based system for this.
Experience with alarms/police
For example: Once, while we were on vacation, we left the garage door unlocked and the wind blew it open. 2 minutes later I got a call from Simplisafe, 2 minutes after that a call from the PD at my house saying everything looked good and they locked my door on the way out.
Overall, I'm happy for the cost. Hope this helps.