Hi, I just got back from booking a Junior Suite on Adventure of the seas Jan 17-21. I did not do the royal up program (booked it with the original reservation so that I could choose my room, as I wanted the room to be close to that of our kids), and had never stayed in anything but an interior room prior. Adventure had the cheapest suites I'd ever seen.
I can tell you the difference between a balcony and a junior suite on that boat are:
1.A bathtub rather than a shower in the bathroom. This was the 1st time I've ever had a bathtub on a cruise and it was deeper then I expected.
2.More space to move around in. We booked an interior room across the hall from the junior suite and it worked well to have the junior suite as a meeting place. It gets crowded in an interior room with more than say 2 people in it. The junior suite seemed like it could fit all of us comfortably. It has a king bed and a seating area with a pull out couch, a coffee table, and 2 additional chairs. There are also 2 chairs and a table on the balcony, and a pull out chair.
3.A walk in closet with a door and light, This was nice as someone could change in there while someone else was using the bathroom.
4.wider balcony, I believe.
I can also tell you that this is an excellent sailing to attempt to bid up. As of a few weeks ago on our sailing there were a ton of open rooms and suites. For reference there is some youtube tours of the junior suite which were exact to what I found in my room.