Kicking - Mixed Kicks, Consistent Message
As people have already suggested, if you race in the 50-100, the 6BK will be preferable. As you stretch your distance beyond that, the 2BK will have equal, then greater, merit in most cases.
What is consistent in both is to (1) focus on streamlining before you focus on propulsion; (2) strive tirelessly to "tune" the kick to your stroke - i.e. to make it blend seamlessly so that an observer would see overall harmony - even at top speed in a short sprint; and (3) to seek the most benefit for the least effort from your kick.
I coached the sprinters at West Point from 1996-99 with results that far outstripped what that group had accomplished before or since. I recall that their tendency when I began coaching them was usually to overkick as they approached maximum speed or effort. Watching from the deck I would see the kick become the most prominent, noticeable part of the stroke. I would urge them to make it blend better with everything else. They would swim faster - and tell me it felt easier.
But tuning the kick was really a minor element in our success. The most important factor in the record-breaking swims we did (we broke 9 Academy and probably as many conference records -- i.e. some records fell several times -- in 3 yrs) was improving start, turn and stroke technique and - particularly in the 100 - learning better pacing skills.
I insisted that all learn to swim the 100 with a maximum of 2 seconds difference between 1st and 2nd 50. Our best swims came when the difference was 1.5 sec or less. We practiced sense of pace relentlessly.
Head Coach & Chief Executive Optimist
May your laps be as happy as mine.
My TI Story