It's changed over time, but way back in the day:
Base80 - it was nice to follow along with text and images rather than videos
Tim Clapham for sure. When I bought R15/R16 he was invaluable and I still buy his tutorials to date.
Vertex Pusher of course.
Cineversity-wise:
Dr. Sassi - for general 3D info and technical deep dives into every aspect of C4D. I've probably watched more of his videos than any other teacher--many, many hours. Tim Clapham comes in 2nd probably for number of hours.
Kai Pedersen - for more practical, specific stuff