Use whichever one you want. Or all three. Or none. Or build from source. They don't conflict as long as they're different pieces of software. Your system generally won't like having the same software installed from the repos, Snap, and Flatpak all at once, but that's about it as far as conflicts go.

The also have different focuses, advantages and disadvantages. It's all about using what works for you.

Flatpak was (is) intended to be desktop focused (which can be seen with Fedora Silverblue/Kinoite), while Snap is better suited for IoT purposes (which can be seen with Ubuntu Core).

Not to say Snap doesn't work on desktop, because it obviously does, but from my understanding, Canonical is more focused on pushing Snaps for server-side and embedded usage. They might make a desktop-focused Ubuntu Core at some point, but it's clearly not their priority.

While they both work (mostly), they have, IMO, different purposes. (For what it's worth, AppImages also have a desktop focus as well.)

I personally prefer Flatpak and feel far more comfortable with it, but people can use whatever.

I've played around with Kinoite and once it matures a bit more, I might end up on that anyway, so sticking with Flatpaks has the added benefit of making that transition simpler if I ever do that.

Really, just use what you're comfortable with, whether it's the official repos, Flatpak, Snap, AppImages, whatever. Stick with one or mix and match. Doesn't really matter what other people do. You do you.