I've stayed at both GF and YC, so I'll try to help you out. The GF offers 2 levels of concierge service. The one in SugarLoaf, called lodge concierge is limited and the main building or RPC is full concierge. There are some small differences. The basic food servings are the same, in the morning you'll have deluxe continental with fruit, different types of yogurt, cereal, breads, muffins, pastry. For early afternoon, you'll typically see a light lunch offering of assorted hummus, a light salad, stuffed chicken breast, vegetables. Then they move onto afternoon tea with scones, trifle, cookies, brownies. The evening offering is cheese & crackers, 2 hot dishes like spring rolls and mustard chicken tenders, mini hot dogs. In the main building you'll also have a wine and beer offering with dinner. The lodge does not offer alcohol and this last serving typically ends at 7pm. The main building has one final offer from 8-10pm of desserts like chocolate covered strawberries and pastries along with Baileys, Kahlua and other cordials. Throughout the day, you are free to use the lounge to relax in. They are both open rooms with plenty of seating. The main buildings lounge offers 2 televisions. Both lounges have cold drinks available at all times. IMO the food offerings were excellent, but tend to be on the gourmet side.
The YC's lounge is very small and it's an enclosed room. The doors don't open until 7am, but at 6:30 they do put coffee on the table outside. For breakfast, they had assorted cereals, fruit, danish, croissants, donuts and bagels. A carb lovers dream. This was available until 10am, then they shut the doors. They re-open the lounge from 11am-4pm. The offerings are gummy worms, goldfish crackers, assorted nuts, cookies and snackpack puddings. Cold drinks are available and sodas are stored under the cabinet. At 4pm, they close up again and reopen from 5-7pm. For dinner offerings, I noticed soup and a beef with onion dish, cheese & crackers, veggies & dip, pb&j uncrustable sandwiches, wine and beer were also available. The lounge would re-open from 8-10pm with mini pastries and cordials. They closed up promptly at 10pm and shut the doors until 7am the next morning. They did have one tv in the lounge, but very limited seating.
Not sure what to tell you about which is a better choice for you. The proximity to Epcot & MGM is wonderful from the YC as is the MK from the GF and Poly. For an 11 year old boy, I would say that regardless of the lounge offerings, they would love the 3 acre waterpark that makes up the YC pool. The GF does offer a theme pool with a water slide and the Poly has the volcano pool, but I think hands down, boys would choose StormAlongBay at the YC every time. Personally, I think the other two resorts offer nicer lounges and better selections, but if I asked my son, he'd pick the YC to go back to.
Tammi