They are completely different. It all depends on what mood I'm in, or what band/artist I'm seeing. I generally like to move around a bit. Plus, you do have to get there early to get a seat. It is tough for me to get there early and either way, it takes me an hour. 9:30 is closer for me. Both have pretty smooth operations and a nice staff. I had a little bit of food at Birchmere, I don't recall it being horrible. I saw other orders, they looked okay. 9:30 has good food, but no where to sit and eat. Either way, both end up being a pricey evening. But with the distance to Birchmere, I assume I'll end up eating there causing me to go broke.
I think I like Rams Head even better than Birchmere - it's a little bit smaller and more intimate with seats closer to the stage. And you can select your seats ahead of time. If Birchmere did that, I might go more often. The both of them are overpriced, Rams Head moreso.