We've done both
DCL and Celebrity and really enjoyed both for different reasons.
If you have children, particularly young children, DCL has better kids programming. Our son liked both the kids clubs, but he likes to spend a fair amount of time with the family. Family time was where DCL had way more options than X. There were so many things DS could do with me or DH, or with my mom, that were really enjoyable for mixed ages, such as the character drawing classes. There just wasn't much like that on X. He was 5 at the time, and napkin folding or cooking classes really weren't his thing.
The food on Celebrity was better. QSine remains our favorite restaurant at sea. The main dining room food was better, and the specialty restaurants were all excellent. (They also permit children in some of them on X. Our son loved QSine, and asked to go to the Bistro on 5 every day for crepes. We would not take him every day of our 2 week cruise, because even the smaller cover charge for the Bistro added up, but it didn't stop him from asking!) We really loved Palo, but honestly, X wins hands down on food.
The ships were both beautiful with art and interesting venues and nooks to explore. We loved both.
A room comparison wouldn't work for us. We were in two low level suites on Celebrity and the Walt Suite on Disney. The Walt wins hands down, but that isn't really fair to X!
(The Walt Suite is actually the only reason we were happy with the food on DCL - we could get Palo delivered to our room. We had a couple of really mediocre meals when we ate in the MDR.)
As far as entertainment goes, we liked both for different reasons. X had lovely small ensembles around the ship, pretty much all the time. It felt like anywhere we walked, there was live music. It was wonderful. Disney had better evening entertainment, and the first run movie theater. We loved DCL's production shows. (We did like the shows with the aerialist on X, however.)
Celebrity has more routes that appeal to us. While we have a toddler, however, we're sticking with DCL.
Anyway, we love both. We would, and almost certainly will, cruise either again.