Ranco thermostats have a great reputation but I can't speak from personal experience. I know several breeders/owners have Ranco thermostats and have great luck with them. I would steer clear of a Helix, personally. Nothing wrong with them, just not the top of the line quality from my experience and a bit of a pain to use as far as setting the temps and what features they offer. I'm currently using a Herpstat II with great luck and would highly recommend one, depending on what you're requirements are.
Ranco, Johnson Controls and Herpstat (Spyder Robotics) are all excellent products for thermostats. Whatever you do, don't skimp on buying a quality one of those. You can get by with a less-than-stellar rack system but your heat control is a big priority. Just my two cents, good luck with whatever you pick! Make sure to post some pics once you get it set up, lol!