Its well established that both Harry Potter and Neville Longbottom could have filled the prophecy:

The one with the power to vanquish the Dark Lord approaches ... born to those who have thrice defied him, born as the seventh month dies ... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not ...

But why exactly did Voldemort chose Harry over Neville?

This may seem like a simple question, but it escapes my memory.