I think it's a bad idea to put 100% trust in using an online site like BitAddress.org to generate your private keys, for example. There are then two points for leaking your keys instead of only one. To have any high level of trust in generating private keys you should use very trusted software, like the Bitcoin-Qt client, which you download locally so the software can't change without you being aware.
the first rule of securing your bitcoin is to understand what it means to secure your coin, and understand how each tool works.
in that sense there is no difference between bitaddress.org and bitcoin-QT (which has been called bitcoin core for years) when it comes to generating private keys. both use good random generation technique to create your private keys and if you use them offline you can call it safe and if it is online then you are not safe.
and by the way bitaddress.org is the online (with web interface) preview of the source code you MUST use instead
https://github.com/pointbiz/bitaddress.org