Fedora or openSUSE Leap for my first RPM distro?

I'd start with Fedora. It gets regular releases and newer packages, which can be handy for development, but you'll need to keep up with upgrades. Fedora releases are supported for roughly 13 months.

For browsing and general coding, either choice should be fine unless your project depends on a particular distro or toolchain. Try both in a live session and see which desktop and defaults you like.

Leap is the one I'd look at if you prefer a longer-lived, more conservative system over frequent major upgrades. It has a different release rhythm from Fedora, so check the support dates for the specific version you're installing.

openSUSE also has Snapper integration for filesystem snapshots and rollback. That's a useful feature to explore, though it depends on how you set up the filesystem and isn't a substitute for backups.

There's a third option if openSUSE appeals but Leap feels too conservative. Tumbleweed is rolling and stays current. Slowroll takes a slower approach, with periodic updates and security fixes between them. I'd consider either if newer software matters more to you than a fixed release.

Don't count on RPM alone to settle software compatibility. Both use the format, but packages can depend on distro-specific libraries or repositories. Check whether the coding tools you need have instructions for your chosen distro. Distrobox is another option for running tools from a different distribution.