There are as many answers as there are different systems. You need to make a list of what you need on your system and what are your dreams.
You might want to check out the yahoo group for homequiltingsystems. There is wealth of information there. Many people have done lots of research and have lists in the data base on that site.
Good luck on your search and don't rush into it. Take the time to do lots of homework and lots of test drives.
Good luck with your decision.