Sharon, I'm by no means an expert, but the reason I believe alot of us are booking on Tuesday is that the first 3 nights (Saturday, Sunday, Monday) we go through our regular dining rotation. Since we don't know what our rotation will be (either APLAPLA, PLAPLAP, or LAPLAPL....I think that's right) we're playing it safe so we can experience all the restaurants. I know one major factor for me was that I don't want to miss the show in Animator's Palate. It's only shown on our first round through the restaurant (so, it's only shown on the first 3 days). Pirate Night is on Wednesday, so we don't want to miss that either. After that, it was just trying to figure out what menu we would miss the least. For us, it was the Master Chef's Menu on Tuesday.
So...since you're looking at Monday and Tuesday, I would vote for Tuesday if you can get a seating. If not, still book when you can and you can always try to change it when you get on board the ship.
For the experienced cruisers....does this sound correct?
Pretty close to the same reason for us. I wanted to go to each of the rotation menus, then Pirate night on Wed and capt's gala on Thurs. That left Tues or Friday for us. I thought Friday night might be too rushed with having to pack and everything ( and I have to go see the pub night show again. It was hilarious!!!)