Ubuntu is a very good all-round distro, a bit heavy on the UI side, but that may not be an issue if your "old" laptop is modern enough. Excellent for software development.

If you want to try a blazing fast distro that actually works on Very Old Hardware, have a look at Q4OS (https://q4os.org/): it's based on Debian and, besides mainstream desktop environments, it runs TDE - a fork of KDE3 that is actively maintained and is extremely light on resources. I use in on a 2003 Compaq Presario powered by by an Athlon XP-M with 1.5GB RAM, and yet it is perfectly usable.