Mullvad is one of the best options if you care about privacy. They take privacy seriously, both on their side and pushing users towards private options. They also support fully anonymous payments. Their price is also incredibly reasonable.
I’m actually working on a VPN product as well. It is a multi-hop system so that we can’t track you. But it isn’t publicly available yet, so in the meantime I happily recommend Mullvad.
I mean it is always better to have more open source. But the point of the multi-hop system is that you don’t need to trust the server. Even if the server was open source:
The open source client is enough to verify this and the security of the whole scheme.