With the sit down longarm/mid arm you are getting more harp space - more space in which to move the quilt sandwich. You are still fighting the bulk of the quilt no matter what. However, there are ways of getting around it, with different hanging systems and what not. Quite frankly, I never liked the idea of moving the quilt while I am quilting. I like moving the machine (like paper and pencil) so I opted for a frame mounted long arm and never looked back. The space in the biggest issue, the beast of a long arm machine with the frame needs lots of space. If you can find the space anywhere in your house - spare bedroom, formal dining room you use once in a blue moon, or a basement, I would go for a long arm with the frame. This is just my preference, and we are all different.