I misread your original title as Top Whumpulance films...which thought was code for movies that featured helicopters involved in rescues. I was immediately going to go with The Guardian, featuring Kevin Costner as a Rescue Swimmer.
As for saddest film, I'm going with Private Ryan. There are some gut wrenching scenes there. Both the beginning, and then at the end. I can no longer watch the tail end when that incompetent fuck does not bring the ammo up, and the dude gets stabbed with the dagger. Such amazing acting, I kept waiting for him to go 80's Movie on the bit and flip the German over and kill him...nope. Honest terror in that scene.
Under the Criteria of best War Film...I'm always going to go with the opening half of Full Metal Jacket. The 2nd half is "just okay"