this is a complicated subject for sure.
if we are talking purely water content the worst one is going to be bananas, it has only 77% water. melons are 95%
in terms of 'fake foods'.. apples were developed to stay hardy and not go bad, plus they put wax on them. so i wouldn't mess with them too much
in terms of digestion some fruits are tough to digest.. cherries, peaches, grapes can give you an upset stomach if you eat too much of them for that reason
always pick organic fruit and avoid conventional