My number one all time favorite, and most watched ever is 'Casablanca'. I love everything about this movie. I've seen it in it's entirety dozens and dozens of times, and have probably watched parts of it while channel surfing hundreds of times. I own it in almost every conceivable format except 4k...and I'll have that too if and when it comes out. It's infinitely rewatchable, and has more quotable lines than perhaps any movie ever. Here's looking at you kid!
It's hard to say what would be my 2nd favorite that I can watch over and over, but I'm going to go with 'Dead Men Don't Wear Plaid' for several reasons. I love classic & noir movies and this one has tons of clips of old movies that are tied in with the story line in a clever and funny way. I think it's absolutely hilarious. It also has Rachel Ward too. And no one sucks a bullet out as well as her!
OFC