Far as fruits go.. oranges are one of the best sources of Calcium (something most of us need a bit more of).. and citrus has tremendous detoxification properties...
From my experience (not vast).. far as the detox potential..
#1. Lemon
#2. Pineapple
#3. Orange
#4. Grapefruit
Frankly... oranges will likely work the best for a longer fast than anything... they are gentler than pineapple and have more calcium... and more sugar than grapefuit.. and taste really good.
I also love carrot and apple juice. I have done short fasts on all of them...
BEWARE OF THE LEMON!!!! POW !!!!!!!!!!!!!
If you can do a lemon juice fast... you are pretty clean...IMO...