Daktronics are my current favorite. Then Watchfire and Optec. Optec's are cheap, and priced competitively. Watchfire and Dakatron are on the same tier, often within a $100 or so of each other's bids, but Dak sells everything with a cellular modem and they have an app for ios and android. Used to be the program was the biggest pain, and they'd try to call you back to train someone else as soon as the first person realized they have no business managing the messages. Now they can download the app and not feel like they are going to break anything, so I'm done after primary power is connected.