What kind of flavour do Devil Fruits have? In the One Piece world, there are so many Devil Fruits having different shapes.
I'm a little bit curious about the flavour of Devil Fruits: Is it different from one to another?

If I'm not mistaken, there's a fruit that resembles Banana or Apple. Do they taste same as their real counterparts?

Is the taste of the Devil Fruits ever mentioned in the Anime or Manga?
Devil fruits taste awful.

This is evidenced by the few occurences we've seen where a fruit has been eaten.

When Law eats his fruit (episode 706):
 

And when Kaku eats Ushi Ushi no Mi Model: Giraffe and Kalifa eats the Awa Awa no Mi during the Water 7 Arc (Episode 271): 



During the same scene Jabra was trying to convince them not to eat it by saying that it tasted like crap:



Based off the several examples of people eating it and saying it taste like crap I can definitely answer your question of how they taste with: Unlike their normal-fruit counterparts, they taste awful.