The puzzle missions are fairly easy to beat on Hard difficulty. As long as you know where to put yourself and your wingmen at a particular time.
More interesting questions might be what missions do people think are the easiest and most difficult. On that score, which missions do people like and dislike the most?
Personally I believe Showdown at the Pass is the most difficult whilst The Wheel Turns is the easiest. The mission I like the most is Ride of the Valkyrie because I just love the Valkyrie gunships and Tomcat's ground base. The mission I dislike most is Slipping the Noose because it was a lot of work to develop and even after having four mission designers work on it, it's still dull.