Should I get an ATT or Verizon IQ Panel 4?

To put things simply, you should base your selection entirely on which cell provider offers better cellular signal coverage in your area. When using an IQ Panel 4, the alarm.com services used with the system cover the cellular costs to use the alarm system. The cost for the Alarm.com service is the same regardless of the cellular provider you select. This means you do not have to worry about getting a SIM card, or cellular plan with either AT&T or Verizon to operate your IQ Panel, so the only difference is the cell signal strength.  

The easiest way to determine which provider has better coverage in your area is to check any cell phones that may use either AT&T or Verizon. If the cell phone gets 2 or more bars of signal in your home, then that cell provider should be sufficient to operate an IQ Panel 4.