I vote Dumbledore; he's a clever schemer.

Dumbledore wants to give Harry his cloak, but decides to capitalize on the opportunity. He delivers it anonymously with a note telling Harry not to trust Dumbledore.

Upon meeting Dumbledore, this allows him to impress Harry by deducing the nature of his cape, and then show his trustworthiness. Furthermore, he can comment on the potentially pure motives of the mud-slinger.

Harry is alternately ashamed of his distrust of Dumbledore, and impressed with Dumbledore's charity and kindness, +2 to Dumbledore.