A lot of it comes down to personal preferences, and the actual individual mango being eaten. Growing conditions such as weather, soil, sunlight, timimg of harvest, ripening time, etc all influence the end result. "The best" mango is not always going to be the best.
That being said, there are general trends among cultivars as far as ranking them is concerned. There is also the strategy of comparing the "best of variety A" to the "best of variety B"
Personally, as far as ripe Asian mangos go, I would say Maha Chanok> PPK>> Nam Doc Mai. I cannot rank Lemon Zest as I have yet to try one at its peak.
As far as green eating mangos are concerned, my favorite is Khun See.