Unfortunately, no independent reviews out there that I've ever found. When I was looking to buy, I went with my experience firing kilns at the community studio and looking at classified ads for folks selling kilns. Our community studio used mostly L&Ls, with a couple Skutts; I preferred firing the L&Ls. Looking at what folks were selling in the classifieds, I found lots of Skutt and Olympia kilns, but rarely an L&L or Cone Art. That told me L&L and Cone Art were either very reliable, well made, and kept by owners or they were mostly used by serious potters who believed a few more dollars up front were the better investment long-term. I bought an L&L from a local distributor (vs on-line) so I could have a local person for maintenance, etc. and to keep the "pottery" dollars local. Well worth the investment. Looked long and hard at the Cone Arts. I've heard good testimonials from potters regarding Cone Art -- especially after Tucker's bought the line back from Shimpo.
Am sure you'll get lots of responses here . . . with pros/cons for every brand out there. Good luck on the selection.