I had a mid arm machine (Bailey) and I rarely used it. It sat, taking up far too much of my valuable floor space so I finally sold it. I never enjoyed loading the quilt tops - at all. In fact, I hated it... so I purchased a Tin Lizzie sit down quilting machine and haven't looked back. I love the 18" harp and I've quilted an oversized queen with no problems at all. It was one of my best ever investments. I have used her a lot.
I'd say go and try out every machine you can... and maybe even take a class on it - there are many available. A lot of quilt shops have them if they have a longarm to rent.. or look for a dealer and take a class just to see if you like the act of quilting on a frame. I personally did not. I was good at it but I really just didn't like it. I prefer to sit and quilt. I love moving the fabric around instead of moving the machine around... and I don't have as much floor space lost to the frame. Those things are space hogs.