This has been a habit of mine for many years. Though what is meant by "lightweight" can be "slippery". People refer to two different things. One is low CPU/RAM usage and the other low disk space. How I think about it is will it prevent the machine from being a door stop?
Or, how well will it run old hardware. What exactly is old hardware changes though; think of Moore's Law, but in a more general progress of technology sense. To cover that, and make this pet project of mine a bit more useful, below are Distros against test machines I have lying around. Maybe it is weird, but I keep old hardware lying around all the time (full specs on my test hardware).
Anyways, it is all subjective, but maybe you, dear reader, can compare your own hardware with mine and decide what to give a try.
What makes up the score?
In the end, its all pretty much "impressions". If anyone tries to imply its more then opinion, well.... I want to be nice. :-) It is hard to balance how much of a modern tool it is vs. does it provide enough tools and stay light weight. I want to give credit when the distro does what the creators want it to do as well. For that reason, I use the default GUI/DE and the default apps initially. I do try other WMs/DEs (OpenBox, LXQT) and the apps I prefer when available.
Anyways, here is a list of things I run through:
Installation process - is it easy / intuitive?
Setting up GUI / environment - can I get things the way I like it?
Browsing App(s) - how well do typical websites load, can I do online email, can I do online document editing, what's up with streaming, etc.?
Media Playback - how well does local music and movies get played?
Media Editing - is it reasonable to edit graphics, music and video?
Office Suite - do the expected apps work for typical docs, spreadsheets and presentations?
Combine it all, stir, pick a number, type it in above. If I have time, my blog may have more detailed reviews of the distros individually.