They are all very similar, though there are differences. There is something in 7up that I don't like. Some are sweeter than others. I don't know if Squirt is still around, but it was less sweet and more sour, though there was no doubt plenty of sugar in it. That Shurfine stuff is cheap, which probably has a lot to do with why I like it. No bloated advertising campaign to pay for.
There was a "throwback" version in stores some years ago, actually with the word on the label. It was supposedly the original formula or something. It was nasty. Can't believe I liked it when it came out, back when I was ten or something. Of course, I usually had a Three Musketeers bar to go with it. <shudder> It's a wonder I turned out so normal.
Mountain Dew has come to be associated with testosterone fueled adolescent behavior, which is probably no accident as it contains insane amounts of caffeine and loads of sugar. Red Bull and that ilk "improved" on it and spawned many imitations.