What is the best tour company to use in Las Vegas to take a day trip to hoover Dam?|142175

I found several on line but I don_t know which to choose.We are going in 2 weeks and I would appreciate any travel advice.

I had friends who used gray lines no complaints

http://www.res99.com/nexres/activities/d��

We just rented a car and drove out there with the guide book.