I have a longarm and also do some free motion quilting on my domestic. For big projects, I choose the longarm, for little things, I more enjoy sitting down and relaxing, being able to move the quilt in any direction because it's not on the frame, so I choose my domestic.
My longarm is 30 inches which gives me far more than enough room. I can't even imagine doing frame quilting on less than 18 inches of throat length.
BTW, my quilter is circa 80's (a Gammill PDQ-30!), has no bells and whistles but I can repair it using parts from Grainger tools. I love it. It is how industrial machines were meant to be! ;-). For awhile I wanted a stitch regulator, but I've heard they can be temperamental. Besides, I prefer that hand-made things have a hand-made look. It doesn't look hand-made when every single stitch is exactly the same length. So now, I shrug about that. I really enjoy my quilter