I gave him a 5/10. He's an awesome driver and I think if he were my personal instructor he'd be very patient and a good teacher. However, he has some odd mannerisms, a high nasaly voice, and in general is hard to listen to as a presenter. For American viewers he's almost a pure stereotype of a tea-and-crumpet Brit. Also, I think he's generally too clinical in his review of cars; it's hard to get a sense of passion out of him and what if any emotion the car conveys.
I don't like that they've isolated him in a corner in the last few series either.
Tiff is a driving god, but I have a hard time imagining him presenting some other subject.