Anything with a gylcemic index below 50 is considered low and above 70 high. Watermelon is over 70, but pretty much all other fruit is below 50 (with a few exceptions...e.g., greenish bananas are ok , but overripe ones are not).
All the berries are well under 50 although from what I can find out black/rasp/blue are somewhat lower than straw--although some lists have blue slightly higher than straw. If you want a snack that is way down there, try peanuts--a score of 10! And if you eat them dry roasted unsalted still in the shells, by the time you shell them you can blow a whole hour of snacking in front of the TV and feel quite full on relatively few calories!
Cherries are among the lowest glycemic index fruits....also grapefruit.
But it is a little ( or a lot) more complicated than that...there are different methods of measuring the GI, plus different people have different responses to the same food (e.g, diabetics vs. non-diabetics) plus different methods of food preparation matter.
That said, plain old berries, eaten by themselves, are generally a good thing!