First of all, because of the Hogwarts Express and the closeness of the parks, I normally recommend getting Park to Park tickets. And, because of that, I'd recommend hitting both HP areas both days. Assuming you're talking about President's Day and the Wednesday after, Saturday the 14th is the 2nd weekend of Mardi Gras. Jesse J will have a free concert on the Universal Stage at park closing and a Mardi Gras parade.
On Saturday, I'd start at USF at Rope Drop, in quick succession hit Despicable Me, Revenge of the Mummy, Transformers, Simpsons and Men in Black as you work your way the long way around the park to Diagon Alley. At this point, check as see if Gringotts is running and has a reasonable line. I'd say if the line is under 45 minutes definitely get in line. They normally overestimate the queue length to account for potential ride resets. As long as the line is undercover in the extended queue out back you should be OK. I would spend time exploring Diagon Alley until 11:00 or a little after. Seeing Celestina Warback or one of the Tales of Beetle the Bard. From there, take Hogwarts Express over to Hogsmead. Ride Dragon Challenge (twice if you like roller coasters as the 2 sides are different). If your group is comfortable splitting up, you could ride Forbidden Journey in the Single Rider Line (possible combined with the Castle Tour to the the theming in the line). From there I'd probably each lunch at 3 Broom Sticks, then make a loop around IOA. Assuming you want to see the Mardi Gras festivities, I'd then ride the HE back over to USF and catch a couple of rides and shows while waiting for the parade and concert.
On Wednesday, I'd start at IOA, Hit Hulk, and Spiderman before making a beeline to Hogmead for Forbidden Journey if you want to take the regular line. Otherwise, use Wednesday and the lower crowds to catch the rides you decided had too long of a wait on Saturday.