Sean Pertwee in Gotham! Michael Caine in the Nolan trilogy is a close second.
(Least favorite: Ian Abercrombie in Birds of Prey, probably because I love how ass-kicking Sean Pertwee's Alfred is. I just can't buy a super refined Alfred any more.)
I am so not a Bartman fan, but I love Sir Michael, so I will go with him.
LMAO just saw that I wrote "Bartman"
I'm sorry. I don't even know who Alfred Pennyworth is. I have never seen any of the Batman movies/shows/etc. (I guess I'll go back to my rock now.)
Michael Caine. I love him as Alfred!