I would easily go with Apollo 11, as opposed to the OP's.
Except the picture that XxDaSTaRxx posted is heavily photo shopped. You cannot see Earth in the original.
The Tiananmen Square picture is no doubt fantastic; and arguably, as equally powerful as the picture I first posted.
But, when you judge as photograph, you have to take in all the elements that make up the greatness as a whole. Where I believe the Apollo 8 pic trumps all others contenders with equal profoundness, and symbolism, is this: the Apollo 8 photo is downright artistic in its layout. You have the foreground, which is the barren desert of gray lunar rock and sand. Then, isolated against the pure black of deep space, is an oasis of color, the Earth. Simply put, it's perfect.