After scrolling thru 21 pages of top fives I'm forced to conclude that most people haven't even tasted the world's best fruit. Probably because they're very hard to grow to perfection. That would be a tree ripened Honey series nectarine: Honey Lite, Blaze, Royale, or Diva. And other similar nectarines. They need to be grown with a long period of water deficit to get the brix up to 24-30. The flavor is unlike anything else I've eaten, extremely rich. Next would be 25-32 brix Bing or similar sweet cherries that also have high acid. The best apricots might be third. Again grown with a water deficit to get the brix up to 24+. Orangered would top the apricot list. Next the best pluots again grown dry to reach 25 brix: Flavor Supreme and Flavor King. Morus Nigra mulberry are wonderful. Summer Muscat grape has a very strong Muscat flavor and is the best grape I've grown.
I haven't had any citrus, tropicals, or subtropicals as good as these but then I haven't been much where the good ones are grown. The citrus I've grown has been good but isn't in the same league as my list.
I love watermelon and blueberries, both very refreshing, but they're way way down on flavor, even the 24 brix Sweetcrisp blueberries I've grown are a distant third.
I've grown and eaten lots of apples and pears but a top five, hardly.
Most commercial grapes even at 25 brix lack flavor. I've grown a lot of these.
Black Madeira and similar figs are great fruit but lack the depth of flavor of the best stone fruits.
So my list:
Honey Royale nectarine
Bing sweet cherry
Orangered apricot
Flavor Supreme Pluot
Morus Nigra mulberry
Summer Muscat grape
Black Madeira fig