I recommend Q4OS if you have an older machine; I learned Linux on Ubuntu because it's popular, but realized over time that having a huge community means there are a lot of clueless know-it-alls giving bad advice to noobs. Q4OS is big enough to be supported, and the focus on stability and keeping old machines running makes it friendly to casuals and oldnoobs who just want to keep using the hardware they've got. There's an .exe installer that will let you plunk it down into your PC without losing anything other than hard drive space.