On the Sun Class ships, Baja and Caribe are the same. On the Grand Class ships, Aloha, & Baja are covered, Caribe half covered, half uncovered, and on Dolphin cabin balconies, they are fully exposed. Check out the pictures of the different ships. The Island and Coral are different breeds and all balconies are different on those two ships
As a general rule, the lower you are, the smoother the ride. Also, from the middle of the ship then towards the back is also smoother.
I booked a balcony guarantee, and was upgraded all the way up to the Aloha deck. What a mistake! I was at the front of the ship and it rocked! I was sick for several days. I wish I would have booked an actual cabin on the Caribe deck and mid ship. The lower categories have less motion.
I am booked on the Aloha deck but towards the back of the ship. I was told to make sure you get a covered or semi covered balcony for Alaska cruising, which is available on the Aloha deck. I have only been on one other cruise and was on an inside stateroom and never even felt the ship move. I have to admit - I am a little nervous now about too much motion. I guess I'll be sure to bring along motion sickness medicine and start taking before we board.