I went to the dragonfruit festival several years ago and American Beauty and Halley's Comet were two of the favorites. I have personally tasted many named and unnamed varieties and my favorites are American Beauty, Yellow DF, Halley's comet and Simon's Red. Simon's Red is just an unnamed variety I got from my wife's parents. I wanted to give it a name so that it can be tracked for future reference. Yellow DF is small but extremely sweet, almost too sweet but its still very good. It's so sweet that it tastes almost syrupy sweet and if you don't like super sweet, you may not like it as much.
American Beauty, Halley's Comet and Simon's Red are all about the same in terms of sweetness and flavor. Halley's Comet is the largest grower in my yard followed by American Beauty(very round and symetrical) and Simon's Red is the smallest being just smaller than American Beauty. Productions wise, Simon's Red produces earliest and the most fruit while Halley's Comet takes a while to fruit and has much fewer fruit. American Beauty is intermediate.
From my experiences, the sweetness and flavor depends a lot on when the fruit was harvested and how and where it was grown. It seems the longer you keep it on the vine after turning red, the sweeter it is but if you leave it too long, the inside becomes mushy. I like to leave mine on the vine for 1-2 weeks after the fruit turns almost completely red to get the highest sugar content and still have the fruit kind of firm. If the weather is hot and sunny, I pick them about 5-7 days after turning completely red on the outside. If its overcast and cold, I let it sit on the vine about 2 weeks.
If anyone would like a free cutting of Simon's Red, I have a couple available for local pick up but you have to give a description of the fruit if and when it produces for you.
Simon