Air-water or geothermal heat pump?

I would be interested in that as well, I am building a 120m² house + a basement of about 60 m². I was advised that a heat pump would be sufficient for these needs without an outdoor unit, all completely installed in the basement. A unit from the brand Buderus would be installed. What would be the difference between outdoor and indoor systems? At a trade fair, I was advised again that I should switch to gas, which would be much cheaper, but unfortunately, I do not have a gas line in the garden; this would have to be added during the development. It would be a KFW 55 house, with filled Unipor 37.5 bricks.

My neighbor put a 69db system right in front of my nose. YOU CAN HEAR that thing, and not just a little!! I don’t blame our neighbor for now, the installer shouldn’t have done it that way. But in the end, he’s the one who’s responsible. What I want to say is: Of course, there are good pumps, but there are also very bad ones. But which builder recognizes that when signing the contract??