I think it depends on exactly what it is you're looking for. Most of them have different "free bundles/packages". Tunnelbear is quite popular (specially due to their advertising) among the free users. As a european I personally use either Allertaprivacy or diebestvpn.
But that's mainly because it's what I know and are familiar with. Been meaning to check out some of the newer ones, like the VPN that comes with protonmail.