Please make sure that you download locally the scrips from bitaddress.org and run them in a safe environment; you don't want others also get those private keys.
It's pretty hard to trust all of these generators. Even if you run it offline, there is no guarantee that a vulnerability is added to the random number generator.
Everything rests on the credibility of the developer and the hope that someone reviewed code. Therefore, only electrum or core.
Something like this:
https://www.theguardian.com/technology/2013/aug/15/google-android-bitcoin-securerandom-vulnerabilityThis situation looks like an accident, but also someone can bring vulnerability intentionally.