My wife and I (no kids) have been on both this year. For a bit of background, we have been on 6 Regent/Radisson cruises and 4 Disney cruises. We are 55 and 48.
In April we were on the Mariner itinerary that went to Cuba. We were originally scheduled for different ports and the price was unbelievable (about on par with what we paid for Disney Fantasy in October, but with literally all inclusive - air, bar, excursions, tips), but the itinerary changed to Cuba, much to our delight. This was an unusually low, low fare due to extenuating circumstances regarding the Mariner schedule. Under normal circumstances I would not say that Regent and Disney are comparable in price, even factoring in all inclusive.
This was our first sailing with Regent after many years. When it was Radisson, there was no all inclusive offer and the prices were quite a bit less. I believe Regent has used the all inclusive moniker to vastly increase their prices (over double) for what amounts to bar and excursions (we don't use excursions for the most part). If you think the early Platinum/Gold event sign up is bad on Disney, it is worse on Regent. Since the excursions are "free", the higher end cabins will sign up for excursions just to have them. When they decide not to go, well, its "free" after all. The all inclusive nature of the bars is almost as difficult. Since the drinks are "free" more people get one - even if it is just a virgin Margarita or Pina Colada (pure mix, yuck). Bar service was pretty challenging.
We had a concierge level room (which got us a pre cruise night in Miami basically) on the Mariner, which seemed to equal the Family veranda cabin on Fantasy. This linens were better on Regent, but I have come to like the split bath on Disney. There was nothing special about the Mariner cabin, other than a fancy Keurig style coffee maker and a walk in closet (took the place of the split bathroom). The room stewards were comparable, which is to say very good on both lines. Regular service (non dining) on Regent was ok - it seemed they were a bit harried sometimes - I think Disney was much more outgoing and friendly. This is an area that we both noticed the difference between Regent and Radisson.
Shipboard life is a plus for Disney. Regent has very mundane evening shows, geared for the demographic (more later). The afternoon enrichment lectures are usually very good on Regent, often with Smithsonian lecturers or known Historians. We like to dine late, so upon leaving the dining room at 930, the ship was very quiet. No repeated shows for late diners. On our cruise, the casino was even pretty much a letdown as far as being hopping. Music is pretty pathetic (again, for the demographic).
Food was a definite winner for Regent, especially dinner. The main dining room (Compass Rose), while not Remy, was several notches above Disney, both in selection and quality. They have an offering where one can pick their protein, a sauce (from a list of about 10) and your sides. It is pretty nice, but the regular offerings were too delicious most nights to pass up. The service was mostly outstanding and one is able to request to sit in a particular server's section upon check in each night. The included wines were fairly disappointing, compared to what I remember from the Radisson days, but they were far from plonk. The alternate dining was outstanding and included. The steakhouse, Prime 7, had the best steak I have been served on a cruise. The French restaurant, Signatures, was also very good - both slightly better than main dining, but neither was quite like Remy.
When Radisson changed to Regent and went the all inclusive way, I had a feeling things were going to change, and for this cruise at least, I was right. Radisson, at the time was a move up line from Princess/Celebrity/HAL etc. The prices were only slightly more expensive, but most every other aspect of the cruise experience was several notches above. The change to all inclusive has raised prices obscenely and started tending to longer cruises. This has brought negative changes, in my opinion. I have already mentioned the excursion and bar. The biggest change of all, and I don't mean this to be looked at harshly, is the change in demographics. Literally 80% of the passengers were over 70. While I had great conversations with some of the passengers, there was a certain sense of entitlement, bordering on snooty-ness that just didn't sit well. A large part of the experience (music especially) was slanted to the older clientele. That simply was not the Radisson we were accustomed to for 5 cruises.
Perhaps the Regent cruise was an anomaly and I am being overly critical, but I would be hard pressed to consider it again unless I ran into a GREAT price. Their current price offerings are far from that. I much preferred our
Disney cruise because of the liveliness, plenty of activities for kid-less adults and the Disney experience (I still really like it). All in all, we paid about the same for both cruises including our room charge on Disney, but we got a ridiculous price on Regent. Normally, Regent would have been quite a bit more. I left the Regent cruise slightly disappointed, but left Disney happy as usual.
I hope this helps somewhat. Questions welcome.