I've got the TireMinder system. It works well. What's impressed me with them is the customer support and service. I've had mine about 4 years. After two years of owning it, I switched rigs and was having trouble pickup up the toad sensors. A phone call to TireMinder and they promptly sent me their new style booster. Problem solved. About 4 weeks ago, I had the main unit start acting weird, it would randomly shut itself off after 5 or 10 minutes. Another call to them and they sent me a new main unit. That's after having it for 4 years!
I can't compare it to any of the others since I haven't owned them, but with customer service like that, I'll stick with them.