I've been on both.

I was on Princess a number of years before Disney though, so a lot has probably changed.
You mentioned the loyalty programs of Princess, and I have to say, it is nice to be rewarded. One neat thing is because we are past Princess cruisers, we got returning cruiser benefits on our next cruise which is on Holland America. I think the group is called the World's Greatest Cruiselines, and if you have been on one of the ships in one of the fleets, your ability to book at special prices and onboard credits and such carry over.
The food on Princess, I'd have to say, was much better and much more plentiful. We had course after course with separate menus for each. Very fancy and elegant, but again, this was a while back.
The cabin was a good size, the public areas nice and everything was beautifully maintained. Tons of pool chairs and very gracious service.
My husband and I went without kids and I remember one of the staff saying they only had the children's staff onboard if there were a certain number of kids set to sail that trip. It may have changed since then, and I feel sure more families are cruising now. Off season, if they have not changed the kid's policy, it could affect some families.
Princess goes to great ports. Very different often times than the stock ones Disney visits. We went through the Panama canal on princess on a 14 day trip. It was heaven.
I am leaving on a Holland American trip in a week or so, and will compare the 3 when I get back. I would absolutely try a different line if you have sailed on Disney in the past.
DCL was great, but so are a lot of others. For a family with active kids or a family whose children typically stick with them in a resort setting, I think there are a lot of choices that make a lot of sense, both for fun and finances.

While not Princess, but HAL, we have booked a Superior Verandah Suite, the third category from the top, for less than Disney was charging the same week for a category 12. There really is a huge premium in pricing for Disney.