I see you have only two different answers so far. which is just not playing the game. i'll give you another two; there are at least 15 "best lightweight linux distro". For your use, I'd pick any one at random, try it out on a bootable usb.

Personslly, I'd try stock debian and choose LXQT for a lightweight desktop.

puppylinux also deserves a mention, I always have a bootble PL usb lying around somewhere. Its reliable , fast for a usb, very good potato-compatibility, has loads of useful programmes and utilitiea already in there. I've never actually installed it permanently though. Scared of making a commitment to slackware that I don't understand.

I'd avoid Damn Small and Tiny Core though - unless you really need them. Cool as they are they are well out of mainstream.