i've owned a BD in the past and it's a great car!
have nothing bad to say about it. very smooth, an awesome corner speed. well thought of design which i think stems from yokomo's years of success with belt driven desings (BD seems like a well refined mr4-tc of old).
i havnt owned a cyclone but have had a chance to try one out. car handles very well and truns on a dime without breaking rear traction (with the right set-up that is ... ).
you cant go wrong with either car though....
whatever you choose, you're sure to get a fast car that'll be toough to beat on the track.