Pirates at MK: always use the right, it looks like it turns away, but you are only going over the water and goes into a shorter walkway.
Space Mountain at MK: always go left. the line is no different, but there are two more drops and better hills on the left side.
Tower of Terror at MGM: Always go left after entering the "basement" area after the cut scene movie in the library. The left line is shorter to the elevators, but there is only two elevators on that side, while there are three on the right. If the left line is moving quicker, go with it...if they are the same, go right; you will get on faster.
Dueling Dragons at IOA: it depends on which coaster you like better. its not a left or right choice.
Hulk at IOA...screwed either way
If I have never been on the ride, I tend to go towards which ever line is shorter; I learn my lesson if I get it wrong and either take the one I like or hope I get directed to the line I like best when there is an attendant
By the way...good, albeit odd question Robert.
...or thats what I tell myself!
And i will watch people who get in line at the same time and then go right and for the most part i would say that the leftside moved faster, some times alot, so that is my unscientific study results (lol).
In the line for the Jungle Cruise at DL, the left side boards on the back of the boat meaning it's a shorter line slightly. And then you also board both the left side of the boat and the center seats. That also has you facing the right side of the boat, which I feel has the best view.
So the left side of the Jungle Cruise line at Disneyland is better.