I think of thread as an extension of the design process. Pick the right one for the kind of quilt, quilting design and texture you are looking to get in your quilt. I use all of them, including glide, signature, A&E, superior, etc. I also use all fiber types of threads: cottons, ploys, blends, etc. For me, I let the quilt tell me what kind of thread would be best and then go from there. I run them all, and they are all great :-)

I have a VERY old HQ16. I do not have a bobbin winder. I use Bottomline prewound bobbins and Connecting Threads Machine Quilting thread on the top (I think it is called Essnetial. I am VERY prolific for charity quilting and just cannot afford those lovely other type of threads.

Try these:
http://www.metroemb.com/store/

VERY inexpensive. Marketed as embroidery thread but works wonderful in a LA. Less expensive than CT essential and a much nicer thread IMHO. They also sell prewound bobbins but I don't think they offer them in the Jumbo M size. Not sure what the Sweet 16 uses. If it uses L size I would look into their bobbins as well.

Thanks everyone- appreciate the input! When I "come up for air" from my machine, I'll try to keep you up on how I'm doing!

Superior threads, call them they'll help advise you. First thing I did was order some of their thread charts. Also love Fil-Tec's Glide and their bobbins if you are looking for shine. Starting to not use so much variegated. It can disappear into matching colors on quilt top and look like a mistake. Superior's So Fine is one of my favorites. But as mentioned above it depends what your machine likes.

Threads and sweetsixteen
 

I just got my Sweetsixteen and am having some tension problems. Doesn't using two different threads in too and bottom bother the tension?

Top and bottom.

You can always use different threads in top and bottom, provided the tension balance is correct. You might want to experiment with Jamie Wallen's method of loosening bobbin thread as much as possible first, then adjusting top tension. This works with domestic machines as well as longarm, and works with any combination of threads. Some machines are finicky about what threads they like and don't like; experimentation typically results in threads that you want to use and some that you might want to skip. Here is a link to the Youtube video:
http://www.youtube.com/watch?v=Q1mRhcquZTM