I've been on Harmony and Allure and I do like Allure a bit better. It may be Amped by the time 2022 rolls around but currently it's the only Oasis class without Abyss. Not having Abyss makes the sight lines on the Boardwalk and in Boardwalk balcony much better. There's also a kids pool so that's a plus.
I like Giovanni's more than Jamie's. YMMV on that.
Now with that said you'll miss some of the amenities you get on Harmony. Allure doesn't have RFID cards, and there are no USB ports in the cabins. And casino ventilation is better on Harmony.
(edit) and somehow I forgot that Harmony has waterslides, but I don't think there is a pool in Solarium?
Allure was nice, it was supposed to get "amped up" like Oasis did this past year to closer match the other ships, but Covid made that not happen. Regardless, it's missing some of the newer venues and slides, but is still really nice. We went on it in November of 2019 and it was still great. I'm mixed between the newer style (Harmony) and the older (Allure) both had their pluses and minuses.
I was looking forward to them adding the sports bar but I imagine I'll still have a blast. About $2,100 for 2 people with a balcony room...real nice deal