Get USB-C if you're buying a new phone - it's becoming the standard everywhere and you'll find charging cables and accessories basically anywhere, whereas Lightning stuff is getting harder to find and more expensive.
For actual daily use, the main practical difference is that USB-C is faster for charging and data transfer if your phone supports it, but honestly the speed bump only matters if you're regularly moving big files or charging from dead to full in a hurry. More important is the ecosystem thing. If you've got Lightning cables scattered around your house, in your car, at work - that's a real convenience factor. But if you're upgrading anyway, switching to USB-C means those old cables become e-waste and you're starting fresh anyway. USB-C chargers are genuinely cheaper and easier to replace, and most of your other devices probably already use it (laptops, tablets, headphones), so you'd have fewer cable types to juggle.
The "stick with what you know" argument doesn't really hold up here because you're not keeping your current phone long-term - you're picking a new one. By next year, USB-C adoption will be even more universal, and sticking with Lightning just locks you into a shrinking ecosystem. Make the switch.