Thanks for your input guys! I will have to check the window position and walls next time I go. I'll also take a temp gun with me and check which room is warmest... It is empty now so I don't know if I'd have the opportunity to ask the previous owners.
The room downstairs is on two outside walls (corner) I believe 1 or both of the rooms upstairs are only on one outside wall.

The downstairs room is close to the laundry room (has access outside into the yard) and has it's own bathroom I could use for cleanup... It sounds like convenience and temp stability might be at odds here... This will take some thinking.