If I was to only ride it one way I would have to say from Diagon Alley to Hogsmeade. Reason being you get the whole train station feel and with running thru the brick wall at gate 9 3/4. Im not sure if the movie was better either way but the station is a much better experience in Universal Studios Hogsmeade
As far as olivanders, they are the same more or less to us, again and not to sound like a broken record but Diagon Alley one is just so much more immersive. That is the one we do, last time my daughter was picked for the wand. It was a cool memory, but was forced to buy a second wand for her "because she had to have the new one that chose her" lol
I'm glad we're hitting Diagon Alley first (that's the one in Universal right, not Islands of Adventure?) -- It sounds like that one is a little more immersive and we won't feel restricted with our time there since we'll just be arriving. Hopefully we can catch it not super crowded at first open.
Thank you so much for your help!! There's just not as much information out there about Universal. If anyone has any other tips on Universal must-dos or anything, please feel free to let me know! (Don't know if that's allowed on these Disney boards though...)