I believe it should wind from the back with the stacked thread (vertical spool pin). At least on my 2 machines, if you pull from the front, it then gets a kink in it as it goes through the first hook in the thread run because you're pulling the thread backward to the first loop rather than forward.
For the crosswound (horizontal spool pin), typically it shouldn't matter because the thread is being pulled straight over the tip of the spool. I usually load mine with the thread pulling from under the spool because I find that easier, but it really shouldn't matter. Of course, we all know that some machines are just finicky & will work better one way than the other.