Silva most definitely needs work but Roach is a great guy to go too if he wants to become a good boxer.
Roach has worked with BJ Penn and other MMA fighters, Anderson Silva is working on his MMA career, as usual.
Dave Beneteau worked with Emanuel Steward before losing in UFC VI. I haven't heard of Dave engaging in any professional boxing matches.
Silva wants a boxing type payday. He could take his celebrity into a big fight and make 10 times the amount that he does in the UFC and then completely retire. (OR he could fight 10 more times in the Octogon for the next three years.) I would choose the payday.