I guess I'm a little different from most responders - after all of my testing, I discovered that a sit-down quilter was the best fit for me.
Partially due to space constraints, but also because I have a bad back, and standing at a LA rapidly tires me out. It's not only the standing, it's the pivoting as I quilt. Whereas sitting at my machine, I can quilt for hours at a go.
I got the Bernina Q20, which is essentially my dream machine. I have had it a few months now and I adore it. Zero regrets. The stitch regulation on it is, IMO, the absolute best that can currently be found on a sit-down machine. I love it. My quilting is already better - between the larger space, the regulator, and the ease with which I can use rulers...it's a blast! I have so much more fun with my quilting now.
Ultimately, in a dream world, I'd have both. I certainly find the "no more sandwiching" aspect of a stand-up LA to be very appealing! But I think a lot of detail and fill work, I would continue to do at my sit-down machine where my back would be more comfortable.