Typically, the calmest geese are the worst alerts, and the best alerts are the most aggressive.
I also would not get geese assuming they will care about your chickens. The wrong goose could even be a danger to your birds.
I have ducks and 2 female geese - 1 African, 1 Buff. They’ve both come a long way to get used to my ducks. Right now, they will at most tolerate being about 5 feet away from them. My African especially will chase and bite my ducks if they get too close, so they must sleep separately from them.
My neighbor has male & female Chinese geese, and while they’re technically kept in the same area as their chickens & turkeys, the geese keep to themselves and choose to sleep separately. They are fantastic predator alerts, but they only guard each other.
I’d do Greylag breeds (Embden, Toulouse, Sebastopol, etc.) if you want the best chance at calmness. I’d probably only get Swan breeds (African & Chinese) for their alertness if you are capable of separating them.