if it is your first time, I would lean strongly to the inside stateroom. You don't know what you are missing first off... and the difference could be used to have fun on the cruise... especially if you are going on the 4 day... you are so busy trying to do everything, you are hardly in your room (at least that is how it was on my first 4 day) By chance I ended up with an outside stateroom (Deck 1, so we had the two small portholes) and I think we looked out them a total of 2 times (The first night when we were having gale conditions, it was rough, but it was SO COOL seeing the waves crashing against the window) and then for like two seconds in the morning as we were getting ready for our day at Castaway...
I haven't been on a 7 day (Yet) but I would probably go for the inside, and save the money for fun at port and on the ship!