"If you're using things like a single hop VPN to do things in a so-called "anonymous" way on the internet, you should probably stop." "When you are using certain VPNs, the NSA has special traffic flow analysis software, for example, that will mark you, put it into a database, and later when an analyst wants to compromise you, they can just pull it out of this database." Jacob Appelbaum in a talk that you can watch here:
(watch from about 2:15 for these quotes) Unless there's a practical reason not to use Tor on top of your VPN connection, it's really best to use Tor (excellent though VPNs are for things that Tor cannot do).