I'm not sure about which free VPN would be best... but I would caveat using a free VPN, as there must be a reason they are doing this for free. Are they sniffing your traffic to try and gain access to your credentials, are they injecting code in to pages for advertising, etc...? I'd be wary when using a free VPN service.
The only exception would be a "free" VPN service that comes with an anti-virus subscription. I had VPN access included in my Kaspersky license, although it was limited to a low data threshold. I'd have been reasonably happy to use a free VPN like that.