While many of these providers say they don't keep logs, when the shit actually hits the fan and lawyers and cops swarm the provider, it often ends up being a completely different situation. You have to control your own privacy, don't trust a single party to protect you. If you do, be aware of the risk you're taking and that you're putting all of it on that one person/company.
If you want to hold privacy closer to yourself and trust a network which is resistant to "malicious" proxy servers, check out the Tor Project (torproject.org)