Solid planks are sometimes even cheaper than parquet because only one layer is processed, whereas parquet often has 3 layers.
From what I've seen: Often the "Select" grades are the calmer ones. "Rustic" then the more lively ones.
Exactly, solid planks made of soft coniferous wood (pine, spruce) are quite inexpensive. The floors can be made more durable if you order them brushed or brush them yourself. This way the soft wood is basically brushed away and the harder annual rings remain. At least that's how it was explained to me by our flooring supplier.
The distinction between select and rustic is also correct. I like lively floors, so the somewhat cheaper rustic suits me.
For the upper floor, we decided on somewhat more expensive ash planks. They are almost as hard as oak, but (ahem) not as ugly :D I just don't like oak at all.
We haven't installed them yet. But for me, they are the nicest wooden floors so far. They are brushed and oiled, 20mm thick, 13cm wide and between 50 and 200 cm long:
[ATTACH alt="IMG_20220812_172507.jpg" type="full"]75040[/ATTACH]
Oh, and we paid 82 € per sqm, just for the wood. Considerably more than we wanted, but well. On the other hand, these things last forever. I checked recently, and just a few weeks later they already cost 110 €.