As I prepare for the GMAT, I realize the kind of English we generally use is absolutely different from what is considered correct on the GMAT. Here's an encounter with one such sentence. Normally, we'd say something like

He's better than me .
But somewhere I read the sentence above is incorrect and the correct sentence is

He's better than I .

Can any expert shed some light which of the two sentences above will be considered correct on the GMAT?