Hitman Hart: Wrestling With Shadows hands down.
This documentary chronicles Bret's last year in WWF, we get see all the events leading up to Survivor Series 1997, and the aftermath. It's truly a great documentary. Plus, the DVD version I have comes with a bonus disc documentary about Owen hart, which is also very good, and there's an interview with Bret on there that seems to be pretty recent. I strongly suggest any wrestling fan check this out if they ever get a chance.