Viper, for the following reasons.

1. Itis incredibly quiet.
2. It is very secure in the tree
3. Very easy to climb with and very light.
4. It is just Oh My God comfortable.

I looked at the Razor as well, but I didn't like the adjustable climbing rail. I have no use for the 180, I have no reason to face the tree. I also don't like the open front stands because when you are climbing, you hang on your arms. The others are sit and climb, very easy.