Underfloor heating and gas condensing boiler?

Since I want to install underfloor heating soon, I would like to know which pipe is best suited for this. The multilayer composite pipe, the PE Xa pipe, or the PE Xc pipe. Which size 17x2.0, 20x2.0, 16x2.0, 15x1.8 ....?

Furthermore, I need a new gas condensing boiler, I have already looked around a lot, since there are so many manufacturers. Of course, important are high efficiency and a large modulation range. But which manufacturer; Vaillant, Wolf, Viessmann, Weishaupt, Brötje, Elco T, Remeha? I don't know what to do anymore. Wolf is apparently less known compared to Brötje? I was possibly thinking of heating with solar hot water support and a water-bearing stove in winter.

I am thankful for any help.

Since I want to install underfloor heating soon, I would like to know which pipe is best suited for this....Which size 17x2.0, 20x2.0, 16x2.0, 15x1.8 ....?

First, have a proper calculation done based on the room heating loads! Then such questions as pipe diameter, number of heating circuits, laying distance, pipe length, pressure loss, temperature difference, and mass flow will almost solve themselves! ;-)

Regards