I chose Summa in this survey mainly for the positive's I've heard about it from users, seeing it in person at a trade show, and it seems priced well for someone starting out.
I've used Roland, Ioline, gerber s750(years ago), and presently anagraph and allen datagraph. They have all performed well, some better than others. The last three years I have watched for sale ads on ebay and sign forums on the net. Very few used summa's are available, I figure that says alot about their quality in my opinion.
George