We've cruised six times with Royal Caribbean and once with Holland America, so we had some reservations about choosing Tui (Thomson Cruises). In fact, we had sailed twice on the Tui Discovery when it was the Splendour of the Seas.
We took an Executive Suite Cabin with Balcony on Deck 8 for three of us. At a similar cost to a much smaller suite on Caribbean, it was more than large enough, comfortable, really well equipped and came with a spacious balcony.
Aside from the cabin, other positives included the food, which was really excellent throughout and right up to the standards of other cruise lines we have sailed with. We upgraded to the Premium Drinks Package, so enjoyed decent premium brands, cocktails, etc, throughout the cruise. Service at the bars isn't always very fast, but this is more down to the bars being busy than any other reason. We found the staff throughout the ship, especially in the restaurants, to be excellent.