I love my sitdown sweet 16! I have tried long arm machines, and I just prefer the sitdown versions where I move the fabric instead of the machine. I've only had mine for 8-9 months, but I've done a lot of practice work on it, 5 quilts, and 3 or 4 table runners. It is soooo much easier to FMQ on the S16 than my Bernina 440. I have used a variety of threads on it - Isacord, Superior So Fine, Superior King Tut, Yenmet metallics, Aurafil, and Gutterman are the ones I remember - without any problem. I generally use a Superior SuperBOB prewound bobbin just because it is easier, but I have also used the same thread as in the top for some of the threads. I've done most of my work with a Warm and Natural batting, but I did some practice squares with 80/20, poly, and even wool. You do have to feel comfortable with adjusting tensions to use a wide variety of threads and battings, but it isn't terribly hard. I use a lot of vintage sewing machines, so it is just second nature to me.
I think the hardest thing to get used to is straight lines. I'm still improving at using a ruler (like the long arms do), and if the line is short I do them free motion but it is certainly not as easy as using a walking foot.
I do recommend a slider to cover the small space between the machine and the table. It is very easy to do the regular cleaning and oiling needed, and I don't find it bothersome.
Pam