Miss Lora by Junot Diaz. I don't know about 'best' but I did just read it (as I walked at lunch - in the new Best Am. Short Stories) and it did make an impression on me. I seem to have a love/hate relationship with Diaz's work.

One interesting aspect of this one is that it is written in second person.
In the New Yorker here:
http://www.newyorker.com/fiction/fea...urrentPage=all
and an interview/Q&A about the story here:
http://www.newyorker.com/online/blog...unot-diaz.html