I'm an oddball, because when I worked on a long arm a few times, it just wasn't for me, I felt I was too far away from the fabric, but when I tried out the sit down it was perfect, so I bought a Tiara.
I don't have any trouble with a larger quilt myself, but you do have to baste the quilt when you use a sit down, as opposed to the long arm where you have to load it.
You really need to give both a reasonable trial. It really comes down to whether you want to move the machine or the fabric, as noted above and whether your skills transfer.
Watson