There are TWO, could never pick just one...I LOVED "Public Enemy' one of the best gangster movies ever...and seeing Jean Harlow at the start of her career was very interesting. Side note; in his movie she is only 20 yrs. Old!!!..the other Cagney favorite has to be "White Heat'...I know he's done so many others but those are the two that stand out in my mind...He was so charismatic...his presence on the screen was almost electric!!!I have heard and read that in real life he was rather quiet and almost shy!!I mailed him an autograph request, from a valid address in Autograph magazine, years ago.....I enclosed a stamped, self-addressed envelope, which is a common courtesy....weeks went by and no reply - oh well, at least I tried.....also during that time there was a postage increase....Lo and behold a few days after the increase, I got his autograph, WITH the additional stamp to cover the postage increase...I was thrilled...needless to say that's one envelope I did not throw away!!!