I think its hard single one person, but to sample some that i admire is Ernesto Hoost(kickboxing) (dutch guys rocks), Ajarn Chai (man he never get tired), Vanderlei Silva (his knees are killers).
In my opinion, distance is one of the most important factor in a fight, if you know how to keep a good distance that fits your personal fight style, but of course many factors are important in a fight.
Its a general question, dont meant to really shows whos the best, just in youre opinion, dont matter what factors are relevant for you to point the best, of course if you can point the factors that lead you to the elected guy will be great.