Personally, mine would be where I just suddenly wake up after a night of sleep, on another world. This world would be technologically similar to the early 1900s....think (1900-1912). I also would have where it would never advance much beyond that...no modern world for me thanks. I'll take my backwards barbarity anyday. This world would be four or five times the size of Earth, with only 4 continents, 3 of them being giant continents about the same size as 6 or 7 Asia's put together, and the 4th and final continent being the smallest at about the same size as Europe and Australia put together. There would be various islands and island chains outside of the 4 continents but I would just have them randomized since I don't much care where they are, what they look like, and so on. This world would be a world where Mages make up about 5% of the human population, which would be around 30-40 billion people...or whatever, and well, Mages would be considered the nobility of the world.
I would wake up on a train somewhere in the world and would be the strongest Mage that lived or would ever live. I would be immortal, giving me an eternity to explore the world or whatever I wanted. Also, when I woke up, I would already instantly/instinctively have complete control/knowledge of my Magic meaning no training or practice necessary. Reflexes already honed. I would basically be a one-man-army/country-destroyer if I wished, and the only Mage in existence capable of such a thing. I would have an indestructible/invincible body to accompany my magic being far greater than anyone else's ever would be.
Also, my appearance and whatnot would change every 100 years to something I picked or created to avoid me being outed as the only immortal, though I would be able to delay it indefinitely if I wished. There's more details but eh....not important for here anyway.
Also, quite a few people not answering the question and instead....just talking about wish fulfilment as a genre and/or arguing about it having valid reasons to be scorned as a genre.....
It's like so many didn't actually read the title of the post.