It used to be. They held the record for many years in a row when it moved to The Great Escape back in 1994. They keep the title even on all their trains (where it says "Rated #1 Coaster In The World!").
I think it lost the title a few years ago to newer wooden coasters, however, still ranks up there in the top 10.
According to some other surveys (don't ask where or who), they still do rate it #1... but it's usually #1 wooden, not overall (like it used to be).