Bookwise, I'm not sure. My opinions are constantly changing. Philip Pullman's His Dark Materials trilogy had a massive impact on me when I was younger, but honestly in recent years I've become rather fond of Edgar Rice Burroughs. I've read the first two Tarzan books, which are extremely entertaining, and A Princess Of Mars is likewise a delight. I think what clicnhes it for me is that his works as so escapist, yet in a time when science fiction at least hadn't truly found its footing (though it did exist), and so he's still toying with concepts that may be commonplace to authors and audiences today. Truthfully, I don't read as much as I used to, which is a shame, but I rarely have the time. I still read some YA fiction, since it's an age range that interests me (I'm currently writing a YA novel series myself) but other than that, the last books I read were King Lear and Titus Groan. This is all to say nothing of Tolkien, of course, as Middle-earth's a subject I could talk about for days, just as I could on the works of HP Lovecraft.
For film, I'm also not sure. As with you Funmi, I admire Christopher Nolan's work, particularly Interstellar and The Dark Knight, but I may go with Shane Black. I'm very partial to Lethal Weapon, Iron Man 3 and Kiss Kiss Bang Bang. Edgar Wright also deserves a mention though.
In terms of TV, it would have to be Joss Whedon. While I love his work in other mediums, it's in Buffy and Firefly that his writing shines. His ability to juggle large character ensembles is phenomenal, and even his 'worst' work (often considered to be either Dollhouse or Alien: Resurrection) isn't that bad.
In comics...that's a tricky one. I have a love/hate relationship with comics anyway, since there's as much that annoys me about even my favourite comics as there is that I like about them. The Infinity Gauntlet omnibus is case-in-point: the six core issues by Jim Starlin are truly awful, but the Silver Surfer and Doctor Strange tie-ins are (mostly) a joy to read. I'd probably have to go with Matt Fraction, who did one of my favourite runs of Iron Man, as well as the most recent run of The Defenders, and Fear Itself, which is my favourite crossover event by far. Geoff Johns and his work on Green Lantern before/during/after Blackest Night, and on Flash, also deserves a huge special mention; he comes in as a close second for me.
NB sort of related, but I don't think Stan Lee's a particularly great writer. He's a fantastic world-builder, as seen in Thor's early adventures in Journey into Mystery, but a lot of his other stories feel quite poorly handled. Maybe that's just my opinion.
"Nothing goes down 'less I'm involved. No nuggets. No onion rings. No nothin'. A cheeseburger gets sold in the park, I want in! You got fat while we starved on the streets...now it's my turn!" -Harley Morenstein