If zero or one threads are waiting on the object, notify() and notifyAll() do the same. If more than one thread is waiting, notify() only wakes up one of them, but notifyAll() wakes up all of them. You can't control which one is woken by notify().
In practice, notifyAll() is used much more often.
Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.
I actually use notify() more than notifyAll(). It is rare that I have more than one thread waiting on a given monitor. Instead I usually control very carefully what thread is waiting on a given monitor and don't have to worry about interference because the monitor isn't exposed. Of course, that doesn't mean it's right. I am but an infant in the realm of concurrency.