You might also join the online yahoo groups forum for homequiltingsystems. And read, read, read. The other suggestions of going to a quilt show that has many systems set up is excellent. That is how I came to the conclusion to buy a used Fun Quilter by Nolting came about. Enjoy the process! :)
The only other thing I might add is that essentially all the machines out there are pretty good. You just need to talk to people and get a list of what you must have and go from there. Buying a used machine is a good way financially but going with a brand that has a close in service provider might also be a consideration as no machine is immune to breakdowns. Other LAQers are also good source of fixing the little things that go wrong.