I agree with Tashana in that we all have our preferences and ability to fit a machine into our homes. I opted for a longarm on a frame, and of the reasons I prefer this setup is because I don't enjoy basting the quilt sandwich, and I don't have to do that with a frame. My friend has a smaller space to work with and purchased a sit-down machine.
Joes Mom - some of the sit-down machines are midarms and some are longarms. The standard definition that I have heard is that a longarm has a throat that is 18" or more (up to 30") while a midarm is 12-17, and a DSM is smaller than 12.