Erm...wow. The NSA might be a light-year ahead of civilian cryptographers, and they might not. They absolutely refuse to say a single word about it. But the NSA ain't letting the FBI in on the fun.
And I'm willing to bet (and do everytime I use it) that there aren't backdoors to most of the popular encryption schemes (Like PGP and GPG). That's why the FBI and NSA get pissed when citizens encrypt their data. I don't know where you got the "backdoor" idea, but go do some reading on the history of cryptography. Real "strong encryption" has years and years of dedicated peer review behind it and absolutely no "backdoors". Apple's filevault, being proprietary, is therefore almost certainly less secure than an open and tested system like PGP/GPG. Guys like Bruce Schneier laugh their ass off when a company shows them their "uncrackable" "secret" encryption routines. Security through obscurity does not work here. The math makes it ridiculously hard to crack, not hiding what's going on. That said, I'm not really up on the literature for Filevault. It could be based on a tested and proven routine with mounds of peer review.
And then again, the most common weak link is the meat sitting in the chair. Whether it's choosing your own birthday or "password" for your password or being susceptible to "social engineering", it's almost always easier for someone to crack the user than the encryption.