I spent about ten years between NH and VT so I think I have the same perspective as the natives.
Grade A Light is what you sell the tourists. They look at it and think it's like extra virgin olive oil and it's not. It's the least flavorful, but it has a nice light color in a clear glass bottle.
Grade A Medium Amber is what most use for their pancakes, although some like dark. Medium is my "go to" syrup. If I use dark it's for cooking. "B" I never saw, but I believe it's use as flavoring in commercial products more than anything else, but I do know some old timers who did "sugaring" on their own and used it all the time.
I can't abide anything other than the real stuff. To me Mrs. Butterworth is nothing more than dark colored corn syrup with something that if I pretend I can almost detect something which is vaguely reminiscent of maple flavoring. If I'm going out to breakfast and I plan on pancakes I'll take a bottle of the real stuff. There's about as much similarity between  "pancake" and maple syrup as there is between the latter and motor oil.