I've stayed in AKL, BC and WL concierge, and toured the concierge lounges at the YC and BWI.
The offerings at the BWI, YC and BC are basically identical. The lounges at the YC and BC are nearly the same (small and only open during certain hours) while differing in each hotel's theme. I really think one could do either YC or BC and there really isn't any significant difference between the two. I found CMs nice at both resorts.
The BWI has basically the same offerings and schedule at the YC and BC, but has a much larger lounge and the lounge has a view of the Epcot fireworks. The larger lounge and view would give it an edge over the YC or BC in my opinion. The lounge is decorated really nicely, though I am partial to the decor of the BWI in general.
I was most disappointed in AKLs concierge after reading these boards forever and it seemed so many people recommended it. While I liked having the lounge available any time I wanted it, I wasn't into a lot of the food offerings (dunbar chicken skewers, I remember...) I like the dinner selections from the Yachtman Steakhouse or Artist Pointe (such as at WL CL or BC CL) much better. I DID love the African smoothies at the AKL. Still, I preferred the offerings at the Mara than the concierge lounge and would rather spend my money (much less of it) there. Also, we had chronic problems w/ service at AKL. No mention of our birthday trip (not that we needed a party, but a happy birthday would have been nice--it was on the reservation), we were checked out early, our sunrise safari reservations were lost (we had a confirmation number so they got us in), our final bill was incorrect...just a run of problems that we've never had anywhere else, nor in any other concierge.
The WL concierge would be my favorite based on my concierge experiences. Awesome selections (Artist point), lounge always open...extremely nice CMs, towel animals. We were there for Christmas and it was just plain wonderful.
I have always been interested in concierge at the Poly and have read many great reviews of it. Also, I think an MK tower view w/ Concierge at the Contemporary might be great.
If your boys like the Poly, I bet the Poly's concierge would be great. We usually stay at GF, but when we've visited the Poly we are always greeted by a really nice atmosphere and extremely pleasant CMs. We go to Hawaii alot anyway so we find the Victorian theming of the GF more fun than the Hawaiian theme of the Poly, but if that were a draw, than I have definitely heard great things about Poly's concierge.
Have fun deciding!
