This isn't easy to answer, since the only objective response would be from someone who did both.
I did onstage seating, and was in the first row, stage right, in the first upstage seat, and had a great time. At times, I did think I'd've liked to see Rylance's face for one scene, but then 5 minutes later, he'd be doing some pretty amazing stuff with his back to the majority of the audience as he spoke to another actor. It's almost like they staged it to be more of a thrust than proscenium.
But if you do miss anything from being onstage, you certainly get to see so much of it up close, it more than compensates. I do think the upstairs onstage would be less desirable, so I would stick to rows A and B.
Of course, the show was so good, I plan to go back anyway, and am not yet sure where I'll sit.
Now t/d/b/a haterobics on here.