Geothermal heating, who can give tips?

We are currently planning our single-family house (145 sqm) with a geothermal heating system with drilling. Who has recently decided on such a heating system and can give tips regarding manufacturers or what to consider. We are absolute beginners, so please not too technical. But I am interested in everything. So far, we have offers from Viessmann and Lechner Massivhaus, quite a price difference. However, we do not want to build cheaply, but cost-effectively.

Definitely modulating. Nibe and AIT (identical inside) are good. But there are also other good ones. The question is what your heating installer/general contractor installs and whether there is local sales/support from the manufacturer near you.

We have not yet decided on a heating engineer, one requested heating engineer recommends Viessmann, the other Lerchner. That is why I am asking here in the forum if anyone has any tips.

Viessmann is doable, but they are not considered top performers. I'm out on Lechner; even the annual performance factor calculator doesn't know them. More important for an efficient heating system is rather a low underfloor heating supply temperature, e.g., 30°C without a heating buffer tank and without closed heating valves. Instead of drilling, a horizontal trench collector might also be an option. It is also important to clarify whether an internal water storage tank is sufficient for you or if you want a separate hygienic storage tank or fresh water.

The most important thing is to have the entire system calculated correctly from start to finish!

My request has now been moved to the correct forum. Unfortunately, I am no longer receiving any answers. Nevertheless, thanks to the few who wrote. Maybe someone still has a tip.