If you have early entry, start with the park that opens first for early admission for on site guests.

If not, I guess Id start with Hogsmead then head to Diagon Ally like in the books / movies in chronological order. Hogsmead has more rides (3 total). Diagon Alley has more shops (only one ride). Each have 1 restaurant ...both have the ALL IMPORTANT butter beer! My son has renamed it Butter Beer World! LOL