Depends on the dataset available. Usually final odds because that is what is preserved for posterity.
You are right of course. My back testing was more for interest than for any other purpose. And the bookies models are obviously optimising for other outcomes than mine.
For sure, there is still incentive for bookies to start with a price that is close to the ending price. And if you base your picks on a 'late' line then that is probably more likely to be a 'correct' line.
Well beyond even that, they're optimising for profit so they are looking for things like setting odds that match popular sentiment when the real outcome probability is significantly different.
You are right of course. My back testing was more for interest than for any other purpose. And the bookies models are obviously optimising for other outcomes than mine.