I have to agree with others; we did not feel crowded on the Allure of the Seas. It truly is a remarkable ship. But if you're not into a ship that big, then I also have to agree with others that the Radiance-class ships are very nice. They are our favorite class of RCCL ship of all of them.
Now, with that said, if I'm simply looking at ships, personally I prefer something like the Royal Princess or even better yet, the new Solstice-class ships in the Celebrity fleet.
But as with everything, it really depends on what you're looking for, your lifestyle, and your budget.