7. Seventh Doctor Curse of Fenric (Amazon Prime, Netflix)
This is one that really holds up better on DVD in the movie version than it does in the televised version. Still, you get the Seventh Doctor (Radaghast, to you Hobbit fans), and Ace proving that they are one of the best Doctor and companion pairings ever. You also get a wonderful, if at times slightly confusing, story that shows the Doctor being a true chess master when dealing with the evil Fenric. The story also has a nicely contemporary feel and, heres a disturbing thought, was on the air the same time as the early years of Red Dwarf and Star Trek: The Next Generation.
Really there arent any stinkbombs in the streaming Who video category. If these ones dont hold your fancy, try a few others. Theres some excellent viewing ahead of you!
Honorable mention: The Key to Time, which appears on Amazon and Netflix, but is incomplete on both, and The Three Doctors, which is pretty damn great, but didnt fit into the scheme I was doing here.