I use a sweet 16 also, I just love it! My dealer is less than a mile from me! I really like the simplicity of the machine, and the fact that the head faces forward instead of sideways. I do a lot of detail quilting and keep my head closer to the work. If the eyelet that holds the thread is bobbing up and down right by my face, it could be distracting or dangerous, so I appreciate that this is not in the way on the sweet sixteen. Yes, it has needle up/down function. You set it to stop either needle up or down, and you can also push another button to make the needle move a single time, either up or down.
I do believe that dealer support is very important, which is why I bought from my local dealer. Since the Tiara and the Sweet Sixteen are the same machine, whichever dealer is closest might determine your choice.
Jamie Wallen's tension video on you-tube is very enlightening, for anyone who quilts on a non domestic sewing machine.
Kathy