The best smoke I've had is NYC Diesel. The best yielder I've had is Nirvana's Hindu Kush. But there are thousands of varieties, and probably no one who has tried them all. And like others said, it's somewhat subjective; some folks like the cerebral high, and some like to be couchlocked. And the actual taste is also subjective.
It's like asking what's the best food in the world. There is no answer to that. You can only ask what's the best food in the world to *you*, and only you can answer that question.