I found this site a while back - basically it will ask you a bunch of questions on your usage of your PC, and will came out with a list of recommended distros, and a list of reasons why YOU could like or not like it.
There are some similar sites to this one, but since I’m not familiar with them, I won’t post them. They are simply DuckDuckGo-able though.
I’d put the 1gb ram laptops to server/kodi/retroarch/something mode and focus on the three decent machines for anything that requires a modern web browser, or add some ram. Porteus might be worth a shot if you’ve not tried it and want to push the Firefox on a potato idea.
I don’t think this is a one OS fits all situation, unless maybe Gentoo.