We have basically sat all over the place. Personally, we like Cat. C seating the best. We have had some bad luck when sitting in Cat. A with dealing with some pretty rude people who feel they can move their chair wherever they want, blocking views or just invading our space. We do like Cat. B seating, as long as you are up in the balcony. If you get stuck on the floor in Cat. B, you are all the way in the back which poses it's own issues with things like people with crying kids just bringing them to the back and trying to calm them down instead of bringing them outside.
The show does still make it's way up to the balcony area, so you don't get left out of the participation. The chairs upstairs swivle around so you can face the main hall while the show is going on and then just swivle around to face the table to eat/drink. I don't think there is much difference in the actual performance from watching in Cat. A to watching in Cat. C, we would rather just save the few extra bucks and put it towards something else on the trip.