The stand up machine is the only way for me. It doesn't mean my stitches are even because I am moving the machine, but moving the machine is far better than having to try to handle the weight of the quilt pulling and catching on everything. I thought quilting small things would be hard on the larger machine, but a friend makes 4 placemats, then lines them up across a single piece of fabric and quilts all of them at once. It's quick.
I agree with the others. Before you invest in another machine, research them carefully. Find out what you want in a machine. My big thing is a stitch regulator. Throat depth is another very important feature. My older Nolting has a 24" throat and I love it. When I do a king size quilt, that roll gets really big. I use mostly pantos and can go up to a 15" panto easily. But when that king roll gets so big, I can still run out of space.
A sturdy frame is a must. If you lean on the frame and it gives a lot, I just don't believe it will hold up well. Mine are metal rollers and they will hold a lot of weight. Go look at the machine you are testing and without it being on, pretend you are quilting from one end to the other. Does the machine hang up on anything? Does it move freely? If you are using pantos, you will need the lazer light. Is it easy to adjust?
What size bobbins does it use? Do you have to have a separate bobbin winder? How easy is it to adjust tension? And, yes, almost all machines have to have the tensions adjusted from time to time. Having lessons is good, but a good manual is a must. Because mine was an older version, I had no manual. I didn't think to ask Nolting for one. I just went to the Nolting website and printed all the pertinent info about my machine and put it together in a binder.
I have only had to contact Nolting once for a problem in the 5 years I have owned my machine. I am so lucky that my husband understands and can set the timing if it jumps time. My older machine has to be oiled almost every time I use it and I keep it really clean. So no service calls so far.