This is a fabulous question and I truly enjoy being on every one of them!
I think it is Allure for me-- fond memories of that ship and its offerings. We had an unforgettable low-key summer cruise that was just absolutely perfect. I have been on Harmony and Wonder as well and love the Oasis class, but my mind goes back to Allure and we'll be back on next week!
However, I also very much enjoy the different style on Anthem and I cruise that ship over and over due to proximity (love the Hershey kiss cabanas in 270), but not nearly as many options for dining like on Oasis.
Finally, took a Jewel cruise to the Greek Isles and that ship has a special place in my heart. While smaller, it was a great ship and crew and I will always remember my time there.