I'd recommend either Linux Mint or Ubuntu. Ubuntu MATE 16.04.3 if reliability is a prominent concern.
And if you're really aiming for the smallest possible footprint, your best options would probably be, in order, Lubuntu, Linux Mint, or Ubuntu MATE.
Question. If you don't know anything about Linux, why not go with Windows 7 / 10? Chances are, you know a little bit more about Windows than Linux.