Who is your favourite director, why, and what do you consider their magnum opus?

[Soundwave]

My favorite "mainstream" Hollywood films of the last say 40-ish years are

Terminator 2, Jurassic Park, Braveheart, Titanic, Dances with Wolves, Gladiator, Shawshank Redemption, The Matrix, Die Hard, LOTR trilogy ... yeah I'm unapologetically a lover of the big blockbusters when they are done well. Then I have a soft spot for screwball comedies like Wayne's World and The Wedding Singer. If you want to count the 70s/80s then add The Godfather I/II, Rocky I-IV, Star Wars OT, Back to the Future Part I (sorry Pt 2 and 3), Ghostbusters I (not II), Aliens, Coming To America, Close Encounters, Indiana Jones OT (1/2/3 only). 

So I suppose in that sense, James Cameron is my favorite director as he has two films on that list whereas everyone tops off at 1. Spielberg would be close I guess, Catch Me if You Can is a film I enjoy so that with Jurassic Park would tie him with Cameron, but I like True Lies too, so T2 + Titanic + True Lies has that beat.

I hate to say it but I hate the cinematographer Steven Spielberg has worked with post 1993 ... I don't like the look of any of his films since then really. Much prefer 70s/80s Spielberg.