FWIW, Mozilla VPN is based off Mullvad, which I've enjoyed for a year to download Linux ISOs and I've never had an issue with. Also they have one of the most anonymous of setups (accept cash, crypto, no username or passwords or personal details required, you're just given a random account number you can add credit to)
NordVPN is oversubscribed crap.
PIA was founded by Andrew Lee, the big brain behind the current Freenode drama, with help of the infamous Mark Karpeles of Mt. Gox fame. I'd rather use something else.