bootable drive

I've made portable linux distros before, specifically with Kali, Ubuntu and Mint. I'm trying to find a general purpose distro that allows me to boot it from a USB with persistence. I know you can practically do it with all of them. But for some reason, when I've made a USB bootable through Rufus...

Here is my situation: I have an older laptop running windows 7 that I would like to upgrade. It was taken offline some years ago, and that is why it hasn't been upgraded until now. I need to take it back online, but first it needs a new OS, and I am thinking of switching to Linux. (I've been...