I didn't do much research on different brands, but I'm happy with the quality of the Teeter 550. For $300 it was a safe purchase for me. I saw some brands for less money, but I didn't have enough information about them to know if they were as good. I just found out about inversion tables on Curezone because I was looking for something to help my back. This seems to be the most popular brand going by all the youtube videos and Ebay. It's a basic model that has a strap to limit the angle of inversion. There is a three position adjustment for responsiveness. When it is set at the most responsive level and the limiting strap is disconnected, it will lock in full inversion. It was a little scary going to full inversion for the first time. It took me a few minutes to figure out how to flip the table back to the upright position.
Sorry I couldn't be much help comparing different brands. The main thing for me was getting a basic model to get the job done. I might have paid more than I had to, but it was worth it for me because it helped my back feel better.