Its a common and popular pick, but I do believe Bruce Lee to be the very best - Movies: Enter the Dragon, Fist of fury, game of death
I have a soft side for Donnie Yen cause he always plays very likable characters - The IP Man series of films would be my favorite of his.
And cant go without mentioning my boy Scott Adkins, who plays Boyka, the most complete fighter in the world.
I used to like Jackie Chan a lot when I was a kid, but I do feel most of his films are dated now, rewatching them is not a great experience. Drunken Master remains great tho.
I guess the same can be said about Van Damme, Seagal and Norris, but those classic campy 80s action films are delightful, even when they are bad.