I use and prefer the Craftsman/Wright/Kobalt plastic rails. They are similar to the Harbor Freight rails, but much better quality. On the HF ones, the clips break too easily, or the detent balls pop out.
I tried the Ernst rails, but found that they don't hold onto the sockets in the heat, the plastic gets real soft when they get hot. Left an Ernst rail sitting on the fender of my Jeep while I was working on it, when I went to pick it up by the rail like I do with my other rails, the sockets just fell off all over the driveway. Thinking that that might be a bit of an extreme circumstance, I tried giving them another chance in my tool bag in my work truck, and I was constantly pulling out an empty rail.