Jerry Andrus--who had some outstanding ideas in regard to flourishes with cards--preferred bridge-sized cards because the ratio of the length to the width was close to the golden mean. My own preference is poker-sized cards because in general I found they are not as stiff as bridge-sized cards, again owing to the ratio of length to width. However, in the final analysis I think the brand of playing cards is more important than whether they are bridge or poker-size. My deck preference for spring flourishes, pressure fans, armspreads, the waterfall flourish et al is Aviator cards, which are mainly poker-size. I don't like the coating the U.S. Playing Card Company currently puts on Bicycle cards.
However, the stiffness problem with Bicycle cards is not an issue with the bridge-sized cards sold by Norm Nielsen and others for backpalm productions.
Most of the cards sold for backpalming are bridge-size, as are most (but of course not all) fanning decks.
----- Amado "Sonny" Narvaez