I think the real secret is that no matter which response you choose--and any of those are good!--you have to have the courage of your convictions.
Are you pushing? No? Then you know better than the other person. Own that. It's more than just not caring; it's trusting yourself to be right, to know that you know your child better than some random acquaintance. Trust that.
Also remembering that what you're dealing with is probably someone threatened by your child's success can help. I find myself being a lot less threatened when I realize that I'm looking at someone who is practicing "competitive parenting." I detest that, and when faced with it, I have two options: play or don't play. If you get defensive, you're playing. You don't have to. You can opt out.
Sometimes a simple, "Huh. <pause> So how about the weather today?" is enough to derail the haters. If you're not threatened, how can they keep it up?
Remember, it takes two to dance that particular little tango! Refuse to dance!
