There is no way to choose between them. I have an R65LS and a K75S. They are apples and oranges. They are generations apart as far as technology, handling, comfort and just overall feel.
It would be like trying to chose between a Porsche 356 Speedster and a Porsche Boxster, same basic design, same function but light years apart in actual practice.
The R65 is quick, nimble, light weight and a blast to ride. But....It is a killer for a long distance ride.
The K75 is quick, can definitely get thrown into the corners and can be just as much fun. I have done 800 mile days on the K75 and wouldn't think of it on the R65.
The biggest difference to me is the technology, The R65 is a different machine when first started than it is once it has warmed up than it is after a hard ride. The K75 is the same from the time you start it up until you turn it off.
I was once told that an airhead is like a living, breathing thing and a K bike is like an appliance, always there, waiting to do what it is intended to do, exactly the same each time.
I believe it. That is why I have one of each.