Jim ...
The best bicycle rack that I have ever seen is the Yakima. Most higher end bicycle stores carry it, problem is that it is a little pricey. If your bikes are heavier, ours are, frankly I wouldn't feel comfortable with the thousands and thousands of miles that we have towed with using that rack. If there is a better one available, I haven't seen it. Needs a two inch receiver to be safe and effective in my opinion.
Yakima.com will select the rack that you need if you give them the make and model of your vehicle ...