My ideal space would be a large bonus room over the garage with lots of skylights... but I have a spare bedroom and I make the most of it!
I'm a very messy quilter so a shared family space wouldn't be ideal for me. I love just leaving my projects as they are and knowing that they won't need to be put away before I get back to them. I also enjoy having a separate space to retreat to so if I want to listen to music, an audio book or just enjoy some quiet. My room is on the main floor and I like that quite well. It could be bigger, but I also think I would just keep filling up more space with more stuff so it's good to have a limit!