What is the most desirable year for the Dart?

If you are just looking at a particular year in general you have to compare apples to apples. Comparing the value of a real 69 M-code Dart to a 71 /6 swinger is apples to oranges.

So lets say /6 to /6 or to 340 (68-70)

/6 or 318 I would say the 68 is worth the most. One because of the potentional for cloning into a 68 S/S Hemi Dart. Two, they have general appeal also. A 68 non running complete car goes for decent money.

Now 340 to 340. I think apples to apples the 68 still goes for a little more. But in 1970 were some desirable options you could not get in a 68. A 70 high impact paint is a big one. Also optional rear wing and hood scoops. Might trump a 68 340 Dart with all the right desirable options.