I have not tried the mountain berry flavor, but I have tried the blue whatever it is (raspberry?), lemonade, and orange. Of them, lemonade is the lightest flavor, the orange is the strongest, but like you I generally prefer the berry over the citrus. They all taste basically like Accelerade. I call it Flintstones Vitamins, as that's what it reminds me of (especially the orange).

Mixing the Orange and Lemonade (or the Blue stuff and Lemonade) does lighten the flavor a bit. I do drink it usually super concentrated to get enough hours of it in my little bottles, though, so it may be relative. Currently I'm working through the Blue Whateverberry and Lemonade Giant Canisters of Fuel, I can't bring myself to buy another one until those are out. I think the lemonade was a good investment to tweak some of the other flavors.

I actually got mine on Steep and Cheap (or Bonktown) but I usually only see Orange there lately, or the caffeinated flavors which I can't tolerate.