I have the HQ Sweet 16 and used my DSM before that. I much prefer the HQ setup because like someone else said, you have a full range left to right and I very rarely have any issues with the throat space. Honestly I don't even notice it, but it would really bother me when it was to the left/right rather than at the top. And what that does is it gives me three sides "open".

And I tend to turn my quilts a lot! Depending on which way I want to go. I don't always work well upside down and that's one reason why I will never buy a long arm. The other is I don't want to constantly be having to roll up or down -- I like being about to squish the quilt wherever I want to go.

I've never even considered trying to change my orientation 90 degrees, but could on the HQ16 except that the table leg would be annoying!

you need to go and test drive there is not one that is best for all it depends on you so go test drive and then make a decision

All excellent advice.

First ... get to a large show and try as many machines as you can, with both orientations. Just like regular sewing machines, and long arms (on frames), you need to get and like the feel of the machine.

Consider the space where you are going to set the machine up. Will you have space at the back of the machine for an extra table or extension? If so, a horizontal (i.e. like a domestic) machine could work. Will you have limited space to the back, but ample space on both sides of the machine? Then consider a vertical orientation.

And yes, there are other considerations as well. If you think you will need support, a dealer local to you will be important.

Also consider ... bobbin size, lighting, availability of a stitch regulator (try them with and without), and other features like ease of speed control, ease of needle up-down switch, ease of threading and inserting the bobbin (some of those bobbins are deep inside and may require longer fingers or smaller hands!! So YES ... make sure you try taking the bobbin out and putting it back in), integrated bobbin winder (preferably with a separate motor), and yes ... cost.

I had done all of my homework, tried several machines (6 or so), and did my comparison spreadsheet. In the end, I purchased the Juki sit-down and I love it.

I had never considered the differences between machines such as this....now I have more knowledge to consider.

Thank you all for your advice..I'll try and find a quilt show soon..

Yes to all of these, and also the ease of using the foot pedal, I was fortunate to go to a large show, spent 3 days trying all the sit down machines, one machine that I really liked (can't remember the brand) loved the stitch regulator system but the foot pedal was small & took much effort to press it down. I knew with my bad knees I could never use it for more than a couple of minutes. The rep was there-I explained the problem, and that it would be a problem for many of us older women. He understood and said he didn't think it could be modified.
I bought the Babylock Tiara, love it! (same as the Sweet Sixteen & a Pfaff-made in USA in same factory, just different name painted on it)

I love my Tiara III
 

I really like the machine on the back side. It didn't feel right to me when I tried them all out at different shops. Having it in the back seems to give me more freedom with my Tiara III. Good luck!