Are you getting park-to-park tickets?
It sounds like you are only planning to do 2 days. Is that correct?
First, I’d check out the crowd calendar at Undercover Tourist by comparison. In my experience, for Universal Studios, their predicted crowd levels were more accurate than the Touring Plans CLs. It might help you decide.
If you have park-to-park, then whichever day you do Universal Studios, normally I’d start by heading to Diagon Alley first and then hop over to IOA for Hogsmeade on the train. However, based on the CLs here, I might make an exception. Head to IOA on Sunday, going straight to Hogsmeade at rope drop while crowds are lower. Then take the train to UOR and do Diagon Alley as crowds pick up…but you’ll be in the lowest CL day then for UOR. After you finish up DA, you take the train back to Hogsmeade and the finish up IOA.
This means hitting UOR for everything other than HP on Saturday. If you get through it, you could of course hop to IOA, or do some of the HP stuff in the evening.
Now, if you don’t have park-to-park tickets, then i feel it probably doesn’t matter which you pick for which day. Best time to hit the park is at opening…so arriving at 11 am means you’ll be arriving for the worst of the crowds. This means I probably wouldn’t do Friday. On the other hand, if you are night owls, you might go ahead and arrive later and plan to stick all the way to closing…crowds lighten up near the end of the day…although not as much as arriving early.
So, without park-to-park, my personal inclination would be to do IOA on Saturday and head FIRST THING to Hogsmeade. Then, on Sunday, do UOR and start FIRST THING at Diagon Alley.
BTW, my advice stands even if you aren’t a Harry Potter fan. The rides are some of the best there even if you aren’t a HP fan. Of course, if you are, all the more you’ll like it.