Whatsapp is owned by Facebook. That automatically disqualifies it.
But WA has been working on interesting proof of concepts for wider deployment such as the client-side encrypted backups. Those are actually fantastic when properly implemented. There's of course shitty aspects with WA about those like the 64-bit passwords, but, if that's a feature Signal thanks to possible collaboration can properly deploy later, I'm all for it.
There's a difference between Signal being categorically better for pretty much everything when compared to WA, but, WA isn't the worst option, even when considering its owned by FB.