The big question is: Do you have a wife? Do you have kids? Is your car going to be 100% secure from them walking by or kids toys/bikes? Those answers will best determine your choice.
I have a wife that walks by plus also gardens so she like to use the garage for stuff. I want protection from her, so I chose the 100% flannel car cover from California Car Cover. They've been around for years. The flannel is thick, soft and cushy so it protects against most light bumps from kids or the wife. Flannel also is not supposed to scratch - I had a black car that I was very picky about not letting get scratched, so I had a flannel then too. It seems like my flannel cover was around $300 shipped.
I'm sure there are other newer kinds and maybe cheaper, but I love my flannel CAcarcover.