I have the Q20 in a table - I've only had it a couple months but so far I love this machine. It's really easy to thread and use, it sews beautiful stitches, and I've so far had absolutely no trouble with it at all. I also like that it takes standard-sized sewing needles - I have not had any issues with bearding. And M-class bobbins are amazing!
However, I'm not sure I'd have bought the Q24 if I'd had space for a frame! I think I prefer a LA on a frame to regulate the stitches based on the machine's movement, not based on the laser eyes that the Bernina uses.
For a sit-down quilter, I was (and still am) 100% convinced that the Q20 is hands-down the best and absolutely unbeatable. (That's why I bought it, after all!) But for a LA on a frame, I think I would lean towards something like a Babylock or perhaps a Gammill. Those are the two I seem to like best when I get to play with machines on frames at expos. But I haven't thoroughly researched either - a frame is simply not an option for me at this time so I haven't really devoted a lot of time into researching them. I just play with them when I get a chance!
Definitely test-drive as many as you can. I test-drove every single sit-down quilter I could get my hands on for two years before I bought the Q20, so I know for certain I bought the machine I really wanted. And I'm very happy with it.