Betharoo ... Larger harp size is makes FMQing easier, though the S16/Tiara offers a lot more space, not in just the harp width but the heighth. There is significant additional height with this machine over a regular DSM. Plus there is little bulk coming off the top down to the needle. So much better visibility.
I've flip-flopped back and forth on this machine ... a big issue to me is how much it will be sitting idle, when I am piecing. I think it's a great machine (have test driven it several times) and while there are other bigger and better machines in this style on the market, it appears to have a pretty good reputation.
Take a look at previous threads here on the QB ... there's been lots posted about the S16 and it will give you a good sense as to what others are saying.
Prism ...you said you would be interested in the Sweet 16 ... FYI it is the exact same machine as the Tiara! ... just a different paint job!
There are at least two others too ... Pfaff and Viking, I think? .... I was just on the HQ site last night and it even has that noted on there (somewhere .. not sure where!)