I use a backless drummer's stool at my piecing machine and a saddle stool that I move between my Sweet Sixteen for quilting and my PC420 that I use for doing decorative stitching. I like the backless, armless design of these stools because that encourages me to get up more often and also, I have found that chair arms get in my way when I'm fmq and also when I'm working on something that requires me to go back and forth between my design wall and the machine.
Like everything, it's a personal choice what will work for you. I'm vertically challenged and found that most of the "supportive" chairs out there are supportive in all the wrong places. Also, sit in them a long time, preferably pulled up to a table where you can simulate all the ways you would move when working. I've found that anytime I go to an office supply store and sit in their chairs they really feel good at first, but if I sit in them long enough I start to notice things that would be a problem for me when working. Sort of like when you're trying to find a new mattress.
Rob