It's important to know (for you) why you're getting a VPN. If you're just trying to get around your countries media filter, then any VPN that doesn't kill your bandwidth will do and you shouldn't worry (...too much) about your identity.
If you're using a VPN to do [WhateverYouWant] without it being tracked back to you, just a VPN won't do anything to mask your activity. Consider this; a VPN just tunnels your traffic to somewhere else. So you, John Doe, with Computer ID 12345 connect to your Facebook from IP {SomewhereInMexico}. Now John Doe, with Computer ID 12345 connect to his Facebook from IP {SomewhereElse}. There's also traffic to {SomeSiteConsideredIllegal} from the same IP..... pretty easy to see it's Joe Doe with Computer ID 12345.
I'm sure there's anons out there more prolific than I on masking activity, but remember to be smart. Get an old computer, put Linux on it, and create the account with a fake name, new email, never log into ANYTHING related to John Doe on that PC. No facebook, no checking your email, no posting in forums John Doe posts in... you're someone different, so be consistent. I'm not advocating illegal activity by any means, but if you're aiming for privacy, remember that simple mistakes can crumble all your efforts very quickly.