The one thing iMessage and WhatsApp have in common is that they both end-to-end encrypt without giving the user control over the keys being used.

So ignoring actual protocol and implementation flaws (I agree with you that WhisperSystems will probably be ahead of Apple there), both rely on the key management being done in a thrustworthy manner.

And this is where I trust Apple more than Facebook, especially in light of the recent FBI events. If Apple says they are not maliciously injecting fake public keys for the purpose of surveillance and marketing, I tend to believe Apple.

If Facebook is silent about this, I assume they are doing it.