I lean toward Diagon Alley which has a bit more to actually do/see.
Hmm. Gringott's (which disappointed me so much I can't really imagine riding it again, and I nearly cry to see the movie with the Gringott's/dragon scene because it's like she had a *proper* rollercoaster in mind while writing it, and Uni ruined it). The train. Weasley's shop. The dark wizard shop where someday I might buy the $300 replica of Bellatrix's dress (I actually wish they had Narcissa's outfit b/c I like her). Butterbeer, ice cream...and you're done? Oh the wand shop, wand kiosk, and the beer place. The rest of it, to me, is watching people watch the dragon, watching people do the spells, and avoiding the singers and their over-loud PA system.
That's MY experience of Diagon. And I like the place, LOL.
Oh and Leaky Cauldron has nothing for vegetarians that you don't have to modify, and it's insanely expensive for bread and cheese. So I don't even think about the place anymore.
I saw a thread on another board where a woman took her daughter and started in London/Diagon in order to do the "HP experience" in the order that Harry did -- ie shop for school. Visits to Hogsmeade by the kids come later in the story line.
You actually have to go back and forth and back. Start in DA, go on the train. Do the Hogsmeade stuff. Take the train. Ride Gringott's.
We prefer to do it in the way that matches Ron's experience. With all those siblings at Hogwarts, he no doubt had been to Hogsmeade before (for graduation perhaps?). I mean, it's just a town. So you start there, then you go to Diagon, and you can go back and forth as you wish.
(DS has red hair and is tall, and it took ages to convince him that he could love his hair and not yearn for black hair, and afterall Ron is one of the true heroes of the books and movies (it was all thrust upon Harry, he has no choice, but Ron and the other friends make choices every day to help Harry), and DS might as well embrace that...and that goes along with following a Weasley path, not the Potter path...that's where that came from)