Hard to pick just one but its would be Risk, Battleship, Stratego or Chess
Mouse Trap fucking OWNS. Operation is pretty fun too. And I remember having Monopoly Jr as a kid.All the current ones I have are kid related since my daughter pick them out:
Mouse trap( I pick that one out actually :side
Monopoly can be pretty fun if you're playing with people that don't start freaking out if the game goes long. I have a couple different versions of it. Red Sox, Monopoly USA and the Pokemon one from when I was younger.Monopoly. Easily. Then Chess. I've never played most other board games.