All the remixes use less memory than the default GNOME edition. To be honest, we didn’t expect that. The last time we did this comparison, in 2013, Kubuntu scoffed the most RAM – and as before, it still uses the most disk. KDE Plasma 5 really has slimmed down its memory footprint impressively, although it’s still no lightweight.
The KDE, MATE, and Budgie editions are quite close in resource usage so in those terms, there’s not a lot to choose between them. That means it’s down to your personal preferences.
All credit to the Lubuntu team: their remix remains the lightest by quite some margin, both in memory and disk usage. Saying that, it does use an old version of the LXQt desktop. There is a repository to install a newer version, but that’s a big ask for a non-techie user.
These differences seem minute and insignificant to me, especially once you start loading a browser with a few tabs or a few documents, and any of these small RAM differences will melt like snow in the Sahara.