If you could craft the perfect scene or scenario to experience in a Star Trek “Holodeck”, what would it be? Would you create a driftwood shack on an isolated tropical beach in which to relax? Would you surround yourself with the colours and smells of an alien spice market in an ancient city on the edge of the galaxy? Would you recreate a perfect time and place from your past or something from a favourite work of fiction? If your imagination is literally the only limit, what would you do?
Too disgusting to discuss in polite company 
Are we talking in the ST universe, or if one were invented today?
I think my perfect ST Holodeck program would be short trips to interact with different alien cultures all over the galaxy,especially ones I couldn’t easily access as a normal human, like gas giant dwellers or deep marine civilizations. But always no more than an hour or so, and no more frequently than once a week, because anything else is a trap.
For a modern Holodeck, replace “alien” with “historic”. Basically, I’d use it as a tourism machine.
Walking the streets of a random city, seeing the people, the architecture, going into the museums and shops, without having to learn the language (universal translator) or worrying about getting mugged. Trying all the different foods without having to worry about drinking the water or picking up something otherwise unfortunate.
Sex. Lots of sex.
Firefly.
Some combination of post #5 and #6.
I’ll be in my bunk.
Zero gravity naked elf orgy.
What? You asked.
My second and third choices would be ancient Egypt and alien civilizations, respectively.
I see it as a way to get outside when you’ve been stuck on a spaceship too long.
It is also a chance to invent places that are impossible in the real world.
I would go to a bike path through a park. And the path does a loop-de-loop. And it’s a Jurassic park. and it’s full of hookers and black jack tables.
This gets my vote as the Post Of The Day. Especially the “I’ll be in my bunk” part. 
It’s a full-rigged ship, maybe a tea-clipper rounding Cape Horn in heavy weather under full sail, but with an expert crew who take such conditions in a day’s work, so the ship is racing along, one of the most thrilling rides in history.
Meanwhile I am down in the captain’s cabin nailing Seven of Nine like a leaky clapboard shack.
Porn aside, I’d have a tough time picking my favorite out of living out a first person shooter, walking through a “real world” RPG, managing a 4x civ-builder, or catapulting large statuesque birds towards shakily constructed towers populated with pigs.
Malacandra: I love you and want a copy of the source code.
The porn’s a given. Moving past that, I’d love to revisit my early childhood but I don’t know where the data would come from (if I could remember it clearly I wouldn’t need the holodeck). Ditto visiting the Mesozoic as it really was; if it was just an elaborate presentation of “Walking with Dinosaurs”, there’d be no point.
As far as scenarios that can be specified, I’d like to any time I wanted visit a cabin on a lake on a rainy day- just sit on the porch in a comfortable chair wrapped in a comforter and just watch and listen to the rain fall on the woods and lake.
Walt Disney World’s Typhoon Lagoon, but with everything “scaled up” to the relative size it was to me when I was nine years old.
Come to think of it, I might want to see my grandparents’ old house again, too, under similar circumstances. 'First house with staircases I ever remember visiting—they were like mountains.
I don’t know why most everyone assumes the sex usage is a given - I’m personally no more likely to want to fuck a holodeck creation than I am a RealDoll or Fleshlight, and for much the same reasons. Actually, less so - I mean, you’re sticking your dick (or being poked by) a combo of force fields, replicators and holograms. Like that can’t go badly wrong - much worse than a little rubber friction burn 
I think being able to jump into almost any movie and live a part would be awesome.
Oh and being able to be a superhero (is that possible?).
Equal parts idyllic surf fishing on a tropical beach, victorious hand-to-hand combat against bad guys, and wild jungle sex with well-built native girls.
Only if the safety protocols fail, and that never happens, right?