If I need to compare yahoo answers to GAG, than yahoo answers will generate very negative answers to any question that "they don't like". So yahoo answers is a turn-off to me. There's no such thing like an atmosphere of helpfulness and friendship like here on GAG. And GAG is also a lot more tolerant towards delicate questions, as long as they make sense. On yahoo answers three quarters of all questions asked in "sexual behaviour" or "sexuality" on GAG, would get very negative answers. Often by one or another over-religious person who thinks he or she must change the world. Sorry if I'm too negative here, but I LOVE GAG and I HATE yahoo answers.
Yahoo answers and Reddit. But, generally speaking, GaG is the best of the choices. I mean, the Qs are usually answered within 5 minutes of the Q being posted as long as it's short & concise and in good English.
Yahoo answers is just full of trolls and spammers, and, on Reddit it's hard to find the correct subreddit to post your Q under sometimes, so you might be bounced about a bit before being able to get the right answers.
Yeah this is the best site yahoo answers is the only other one, but they have changed their rules now where when you ask a question it goes into the this question is being checked by the yahoo community they keep adding and removing shit on that site and it is really gay now.
Yahoo answers and answerbag but they are sort of dead, nobody seems to answer questions on there anymore I asked several questions even a simple test question and none of them ever got answered which is surprising since yahoo answers used to be really active. Just stick with GAG it's like the only good popular Q&A site.