Obviously this question is very subjective, but I can share some I have really enjoyed.
I had a phenotype of "Sins-OG" from a sincity seeds tester batch I grew years ago. The yield wasn't impressive, but the flavor and smell were downright explosive. It was a cross with Kosher Kush, and based on my research I believe that is where the flavor I experienced came from.
In Michigan one time I got to try a strain called "Space Krush" from tri-cloud genetics. I had some live rosin which had amazing flavor, and then later was handed a joint, and it tasted exactly as delicious as the rosin and I knew it was the same strain right away.
I think my number 3 might have to be "lemon-G" from a mystery grower in Ohio. I only got about 2 bowl packs of it, but it was like fresh lemon zest. By far the most lemon strain I've ever had. Sadly I've never gotten it again, or found anything else that was even close in the lemon smell and flavor.
I've also had very tasty phenotypes of White Widow which is a really specific taste, Cindy99 and of course the platinum delight phenotype I've kept for the last 5 years primarly for the intense flavor (and great smoke).