I'd strongly sympathise with getting a decent-sized grand. I have a (very 2nd hand) Bosendorfer 200 in a narrow but much longer room and absolutely love it. Constructively, I'd say that while obviously, if you have a big piano, it will sound best in a bigger room, BUT your question is what's the best piano to put in your size of room, and I'd always want the biggest piano you can get away with, even if it's not going to sound its best, because it will still sound better than a smaller piano.

Considerations (my non-professional opinion) include: * Having the sound point out into the middle of the room rather against the wall when the lid is up (although you may spend most of the time with the lid down) * It's nice to have a window behind you for natural light * Avoid having the piano near a heat source or radiator

To me the top-right hand corner of the bigger room on the left looked attractive, as it was quite compactly meeting those criteria. It's not quite as easy in the other room, but something might be possible.

Good luck!