My favorite Arcade game would be either Tekken (the whole game series) or Street Fighter II. I love those games so they would be my favorite for all time.
Tie between Pac-Man and Donkey Kong. I am a horrible player at them but they have levels of addiction around them which tends to draw in my pocket full of quarters.
I've always liked Joust. My old barber shop from when I was a kid had a Joust machine and I always made it onto the high score list. Really fun game, especially since this particular machine was rigged so it didn't require any quarters.
I'm a beastly Centipede player, though I'm now more skilled at the flash version than the classic arcade version. Pacman is about the only game out there where I'm still better with the joystick than I am with the mouse or keyboard.
Metal Slug all the way. That game is just so addicting and fast paced. There always used to be at least one Metal Slug cabinet at every arcade I went to.