We see this all the time, online news groups, magazines, and toy reviewers give inexperienced opinions about the best water gun for a given year. We all would probably agree that they are wrong and we all even agree on a particular one as "Best" as a community. but how do you come to that conclusion (or would prefer to) ?
First, I would open up the "best" competition to any name brand blasters still widely available ), I.E can be found at most american Wal-mart's, or K-mart's during the warmer months. (Seeing how target has dropped the WW brand.) then it all goes down to testing. (any name brand squirt guns excluded as they are all roughly equal.)
My system which would ignore stats would have a veteran who has used all the blasters applicable to compete for the title that year against all the other competitors that year, in three different game-types; these being Soakfest, OHS, and OHK. He would then rank them by his personal preference, whilst providing a few comments why each was ranked where it was.