If you've created lists within the default Reminders app, there are probably lists that you access more frequently than others. For most of us, that will probably be our work lists. While you can easily switch between lists you can also change the order around to set the ones that you use the most with a higher preference. This way, when you switch between lists you'll see them in the order you prefer instead.
While creating reminders in the default Reminders list on iPhone and iPad serves it's purpose, we've all got different tasks and things to remember on a regular basis. For most, that will be a combination of tasks between home, work, volunteer organizations, and more. The default Reminders app allows you create custom lists outside of the default ones just for this reason.
The native Reminders app on the iPhone and iPad are not only simple to use, it'll automatically sync your content between any iOS device and Mac you own. Along with the ability to set up your own reminder lists, you can also choose a default one. That means that new events you add using Siri will end up in the list you've specified.
Here's how to tell Reminders what you want your default list to be...