Deciding a TTRPG system

Hello, curious how people decide a TTRPG system for a game/story they want to have.

I'd be happy if this kicked off a lot of discussion, but I am wondering more like if you have a type of story in mind, how do you decide what TTRPG system to play it with? Do you use the system you are most familiar with? Or do you use a system that goes more with the theme or setting of your story? What is your criteria to make an enjoyable time for you and your players?

I let the game determine the system used. If I'm looking to run traditional high fantasy, I generally use Pathfinder 1e because it's what I'm familiar with. For a grittier fantasy milieu, I might choose Savage Worlds, and for ultra-realism, I look to GURPS. For science-fiction, my go-to is Savage Worlds, but I've also run and enjoyed immensely both Traveller and Alternity. If I want to play, for example, romantic fantasy, why not use the rules written specifically for such (7th Sea)? Sometimes, I want to try the game system or the default campaign setting itself. I once ran a True20 campaign just to see how the system played. It's not the system that makes the difference, it's the GM and players!

A good question. Sometimes, like WhtKnt I want to try a specific system, and so I choose the story to match our showcase the system - often that's using a default or built in setting.

If I have a specific story in mind, then I try and think what would do I want the players to do at the table? Is there a mechanical need? For example, of I want the players to ride dragons, then what systems don't just allow it but make it shine or be extra cool? If I want a political intrigue game, then what systems provide ways of managing those interactions and evolving relationships?

Of course, there are many answers to these questions but they're good questions to ask yourself: what do I want the players (not necessarily the PCs) to do most in the game, and what system makes that shine?

This might not answer your question, but usually it's the other way around for me. I'll be in the mood to play a certain system and create a story that works with it. :D

This exact question is probably the part I waste most of my time on when working out a game to run lol

Likewise! I know exactly what game system and setting I want to run, it's just a case of finding the right hosting site to run it on.