Satsuma (from an old mature tree), Kishu, Minneola tangelo, Shasta Gold, Page, in that order.
Kishu tastes very similar to Satsuma, and I would say Kishu is a close second, almost tying with Satsuma for first place. Satsuma can be very variable in fruit quality and flavor however. You need to get a very fresh picked fruit from an old tree to really be able to appreciate how good the flavor of Satsuma can be. I find all the different varieties of Satsuma to taste very similar. A Satsuma fruit that is not such good quality can taste not as good as all the varieties listed.
Shasta Gold and Page each have a very different type of flavor from Satsuma. Page has a flavor more reminiscent of Minnealo tangelo but more orange and pine needle fragrance.
This list does not include grapefruits and lemons. Valencia oranges can also be very good, but it is hard to rank them and compare them to the other varieties here, since they all have different flavors.
I have also had the opportunity to taste Lee x Nova, and it is very good, better than most other mandarin varieties, but still at least in my personal opinion not quite as good as the varieties here that are listed. But this could be very much a matter of individual preference. (It has, what I would call, a "standard type of mandarin flavor", which is not the same as Satsuma or these other varieties I have listed)
I've tasted both Lee and Nova, and can tell you Lee x Nova is an improvement over its parents.
I have tasted Dekopon, and they are good to snack on, very sweet, but I personally find their flavor to be too "rich", and strangely it doesn't feel like it digests as well for me. I perceive a very subtle mango flavor in Dekopon as well. This is probably very much a matter of individual personal preference.
Probably much better than most mandarin varieties, but I personally would not put it on my favorite list. The flavor is somewhere between a standard mandarin and an orange.
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