Radiator or underfloor heating: What is recommended under these circumstances?

And what does the BT charge as extra fees for all the other stuff you install as extras in a new build? Are only 20 x 20 tiles included and the laying of 30 x 60 tiles comes with a horrendous surcharge? Larger bathtub, walk-in shower? Ask and then decide, after the house seemingly does not correspond to the costs.

Could the builder possibly be Deutsche Reihenhaus? Sounds a bit like it to me, even though it would be new afaik that you can even choose underfloor heating on the ground floor. If it’s them, don’t let yourself get stressed out here. You can live very well in their houses and you won’t be poor in extras (there are hardly any to choose from). In some places, the standard is surprisingly good. I’m actually a big fan of underfloor heating, but honestly, I don’t know if I would take it under these circumstances. I might even pay the price (I try not to focus so much on individual items but on the overall package and the number at the bottom right), but then only on the ground floor? On the other hand, my parents built exactly like that back in the 70s: underfloor heating in the living/dining/kitchen area, radiators in the other rooms. In my perception, the house has underfloor heating. Not “a little underfloor heating,” not “a mixed system.” It’s simply an underfloor heating house.

So if at all, I wouldn't mix either. Then stick with HK, especially with local heating.

I would, even if you aren't asking for it, not rush anything. Especially not if it is a life decision.

What is absolutely understandable to me is the desire not to commute far. In the Frankfurt area, you inevitably have to make compromises.

With a local heating system with pellet heating, you will anyway be dealing with 70-80°C supply temperature at your house transfer station and probably around 40-50°C return flow. In your case, underfloor heating will not save energy because you can increase the supply temperature on the house side up to 60°C without any change in efficiency.

For underfloor heating with lower supply temperatures, you then need a different house transfer station, which is probably more expensive, which at least partially explains the high surcharge of the BT.

A mixer is also required for the HK. 60-degree supply temperature in the KfW55 is absurd. In the moderately insulated old building, I have a maximum of 45 degrees.

What is absolutely understandable for me is the desire not to commute far.

I can even very well understand that desire. I would also make compromises to save every minute of commuting time. (In fact, I have done that too)

Anyway, in my eyes a mixed installation is basically nonsense. I would stick with HK then.