I don't know why, but I am all about the Glacier Freeze flavor, part of the "Frost" lineup. The regular blue is not so great.
My least favorite is the Lemon Lime, probably because I drank four cases of it as a kid. The old man brought home a bunch leftover from a work event and I was a thirsty 7-year-old. We never had soda or any real prepackaged drinks around the house so I got carried away.
I'm also not a big fan of the G2 low-calorie lineup, except for the grape flavor. Not sure what they did there but works, somehow.