If your computer has only 2 GB of RAM I think both Gnome and KDE are not very appropiate.
If you want to install a very recent version of Ubuntu I would try LXQT, default desktop environment of Lubuntu.
You can install an older version of Ubuntu too. Now with Canonical free offer of Ubuntu pro you get 10 years of security updates. I say that because Ubuntu 18.04 came with LXDE desktop environment which is even lighter than LXQT.
But depending of how you use your PC, LXQT could be light enough and you get a more recent version of software packages. You may have to go through a trial and error process.
You also have to consider that the main consumer of resources is the browser. Among the DEs there may be differences of consideration between those who consume more like Gnome and KDE and those who consume less. So maybe you don't find much difference between LXDE, LXQT and even XFCE (default in Xubuntu).