All of the above questions and answers are good but if you live where you can go look at some Cobras I would suggest that you do that. The problem with buying from ebay and places like that is pictures can look great but the person who built the car may have junk underneath for suspension and such. As for the best kits which may be out of your price range I don't think you can beat the Shelby or Kirkham Cobras. However ERA, Superformance, and I think Factory Five can be built to just about as good as the others. They will just never have the name that the Shelbys and Kirkhams do. The cars are basically as good as the person that built them. Some are great and others aren't to good. So I wouldn't worry so much about the brand as I would being able to look at the car and see how well it is built and if it has the things that you would want. Remember, the people that build these cars build them to suite what they want and like and it may not be the same things you want or like.
Ron