If I were to vote, I think I might have to check every box!
When I'm playing a game I've never played before--or haven't played in a while--I have a tendency to try to stick as closely to the written rules as possible. I want to take my best shot at understanding the rules as written before I go monkeying with them.
I also, though, like to search out any insights from the designers. I think the designers intentions are important to understanding a game, & there's always more that you can learn about that beyond the book(s).
After that, though, I like to experiment with variations. Both my own & some published.
Some experiments last just one or a few session. Some experiments last a whole campaign.
I don't know about "prep methods" so much, but I also experiment with how I run the game. e.g. The classic Traveller campaign I ran a couple of years ago was all about trying a "sandbox" game using the Spinward Marches, 76 Patrons, 101 Patrons, & such (hope I got those numbers correct) & trying to improvise the rest on-the-fly.