Stray away from free VPN services. Personally I use Private Internet Access, but there are plenty of other services that offer similar value. Speed, location of server(s), traffic logging, anonimity, and form of payment.
Has anyone done an audit of the standard openvpn connect app. https://play.google.com/store/apps/details?id=net.openvpn.openvpn&hl=en
I use it to connect to my home VPN server while on public WiFi.