I have a main house with a 200 amp panel. I also have a barn with 100 amps. Also a well, a front main gate, and some little stuff like irrigation. For the main service load panel, should I have a 200 amp service or 400? Thanks!! El

What is the demand load?
Why are you asking this? Is this a new installation? Or are you looking to change something?

Just from that I'd say get the 400 if you can afford it, can't tell where you are, go underground from the utility if you can.

As Stan mentions, you need to have a service demand load calculation performed to determine the size service needed.

Best you hire an electrician to come in and evaluate all that you have, and size the service.