When I sailed on Allure of the Seas not too long ago, I ate at Giovanni's Table (Specialty Italian Restaurant), Windjammer Marketplace (Buffet), and Silk (Main Dining Room). I will just say that paying for a specialty restaurant is very worth it because of the luxurious experience. I still loved the Windjammer Marketplace and the Main Dining Room but I definitely preferred one over the other.
On Allure of the Seas, the Windjammer Marketplace had a wide variety of options, which I deeply appreciated because I like to try new things. I definitely tried small portions of new foods in the Windjammer Marketplace--some I liked and some I didn't. Also, since I was on an Oasis Class ship, the Windjammer Marketplace was absolutely massive. There was an abundance of seating--and even during peak hours, I was always able to find a table. However, I do know that Serenade of the Seas is a smaller ship, so I don't know if the Windjammer Marketplace is as spacious. The one thing I wasn't so crazy about the Windjammer Marketplace was the food itself. It was good overall, but the quality of the food wasn't as good as in the Main Dining Room. I appreciated that the Windjammer Marketplace was casual, fast, and easy. I ate here for breakfast and lunch throughout the cruise and thought it was fine.
However, I definitely enjoyed the Main Dining Room way more because of the experience. I understand why people don't like how slow the Main Dining Room is (yes it is extremely slow sometimes), but it feels a lot more luxurious and the service is top-notch. Silk, the third-level of the Main Dining Room on Allure of the Seas was absolutely gorgeous--it was extremely elegant and it even felt like a 5-star restaurant on land solely based on the ambience. The Main Dining Room on Serenade of the Seas looks gorgeous too. I also found that the quality of the food was much better in the Main Dining Room and it looked way more appetizing. Everything I ate tasted absolutely delicious especially the escargot. My servers on the Allure of the Seas were fantastic, too. My only complaint about the Main Dining Room in general is the tightness and lack of variety for both breakfast and dinner. The breakfast menu offered the same 12 items and the mini-buffet everyday and the although the dinner menu did change every night, a good portion of the menu was offered every night. But needless to say the food was definitely very good.
I found that I liked the Main Dining Room better overall.