My wife and I just finished a 7 day cruise on the Allure and we are booked in April on the Oasis. They are sister ships so if you are familiar with one then you will know the other as well. As they are similiar there shouldn't be any difference between the two. As previously mentioned, don't make your decision based on the show. Departure date and ports of call are what we based our decision on. We have sailed with RC many times and love the staff. Their was a lot to occupy our time on the Allure and so I imagine that will be the same case with the Oasis. My only complaint is the smoking thing in the Casino. We are not smokers and it is pretty bad. Unfortunately if you wanted to head from the Dining Room to the Amber Theatre you had to pass thru the Casino or go up a flight a stairs, cross over and down a flight.
By the way...if you are on deck 7 there is a "secrect door" at the end of the aft hallway, (not too many people know about this), that will take you straight out to the rock climbing area and Aqua Theatre. You can also go down a flight of stairs from there to deck 5 which puts you on the walking/jogging track.