The Two Escobars is the best of the 30 for 30 series that has plenty of good stuff. Once Brothers is my second pick, the end with Vlade going back to visit the Petrovic family... see it for yourself. Unmatched (Martina and Chris) is also really good, for someone old enough to recall that rivalry. Little Big Men, "The one about the Kirkland LLWS team" was the only dud of the batch.
That said when it comes to sports documentaries Hoop Dreams is so far and way the best ever made. I only mention this in case there are people who have never seen this movie. If you have not seen it shame on you, best three hours I have spent in front of a TV. Even if you could care less about basketball you will love this movie.
Watch for free on Hulu, now you have no excuse to miss this excellent documentary.
http://www.hulu.com/watch/249576