The balconies on the Caribe deck are larger than on Baja & Aloha decks, but they are also visible from those above (on Baja & Aloha). If that doesn't matter to you, Caribe would be fine otherwise. If you want a bit more privacy on your balcony, I'd go for the higher decks. (Of course, if you stand at the rail of your balcony on the higher decks, those below can see you - but they have to turn around and look up in order to do so.)
Generally speaking, cabins amidships (in the middle, front to back) have less motion than those on the ends, but I think the cabins at the stern (rear) are a good second choice. Avoid the ones near the bow (front), as they feel the most motion. Sometimes cabins along the very back of the ship are a bit larger than others in their category, but that may be partly because they are shaped a little differently.