I've trained with Anderson Silva, Big Nog, Marcelo Garcia, Ryan Hall, Rumina Sato, Rickson Gracie, Royce Gracie, Dan Henderson, Eddie Bravo, Frank Shamrock and Bas Rutten has been by far one of the best I've ever learned from.
His Stand up and striking is incredible in person. His Ground game is not that bad and he's just a great instructor.
Get any of his instructionals or even his audio tapes (which are hella intense) and if there is a chance to work with him, do it.
Not only is he funny as hell, but you'll get alot out of his training.
Dude is a legend and KNOWS HIS SHIT when it comes to combat sports. If any shitdog.com hater says otherwise, they've never been involved in acutally MMA training, as Bas is one of the best in the business and always been down to earth when it comes to learning and even to meeting his fans.
With that said, he knows what works and what doesnt and he's been in the business for a long ass time, from the old UFC, to kickboxing, to Pride, to IFL, to Elite XC, to MMA in general.