I consider Gene Hackman the greatest American actor of all time. Bonnie & Clyde, I never sang for my father, The French Connection, The poseidon adventure, The Conversation, Young Frankenstein, Superman, Uncommon Valor, Hoosiers, No Way Out, BAT 21, Mississippi Burning, Unforgiven, The Firm, Crimson Tide, Get Shorty, Absolute Power (so good), Enemy of the State, Heist, The royal tenenbaums ... just so many good roles where he does such a great job.
For this, I voted for Jack. I agree with another poster who said that Al is a little over the top in most of his roles. Worked well in Scarface and some others but it gets a bit too unrealistic at times.