I have sailed on both the Oasis and the Allure. Let me tell you that you don't feel crowded on those ships because they have many actvities and people are not concentrated in one particular are.
I have sailed twice on the Liberty of the Seas and that class of ships does have a lot of stuff to do and mkes for a great cruise.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!