Here is a simple guide to determine which one to choose:
1. Does your system have a pump start relay? If so, go with the AC-powered because the DC-powered is known to be not compatible with some pump start relays (however, you can always replace your pump start relay by a solid state relay and DC-powered works fine with most solid state relays).
2. DC-powered is more convenient for customers outside of US/Canada/Mexico where 24VAC power adapter is difficult to source. It’s also flexible for users who want to power sprinkler system off-grid, such as by using solar power.
3. DC-powered is slightly lower-cost — if you are US/Canada/Mexico based, the power adapter is included. For AC, the power adapter is additional.