Best ever is tough - but my DH always wins the "Best Ever" prize. Best lately - two candidates:
1) Am home schooling my 11.5 year old grandson over the internet. (Not my idea.) One morning I didn't feel well, so I IM'd him to start without me (he will actually do it!), and I'd be on line with him around noon.
When I got up, I checked to see if he was online. He wasn't but he sent me the sweetest note! "Oma, I can't wait until you fell better!" I can't imagine many teachers get compliments like that - I expected more of a "Don't hurry on my account." type of response.
2) Grand-nephews and nieces were out for Easter Week. The night before we had to take them home, I asked them all what was thier favorite part of the week. The younger boy, who is in a bad family situation, immediately said, "Being with you!" And he meant it! You know he'll be asked back!