The best fruits for energy are the most calorie dense.
Also there is no such thing as instant energy.
Bananas and dates are a good choice. Dates are fantastic due to their small size and decent calorie density for fruit. Grapes are also another good choice.
There is a reason why bananas are so popular at professional sporting events. If you go to any event where there is time to eat you will find the pro's eating bananas. When people must eat on the go like with ultra marathons they may prefer dates or gels, again because of the size and calories offered.
The reason I also like grapes is because they are also really hydrating.