Have stayed several times (2006-2007) at the YC concierge and we really liked it. The staff was always wonderful and very attentive. Food offerings are varied and good. Drinks are also many and plentiful. The lounge is not huge but very quaint. It can get crowded if there are a lot of people staying concierge but it seems to be much quieter than BC. The turndown service and housekeeping were also great. No complaints.
We have not stayed WL concierge but have stayed at WL. I believe the lounge is similar to the AKL concierge in that it overlooks the lobby area which is very nice. You can do a search and see concierge pictures at both WL and YC. Keep in mind that the rooms at the YC are larger than those at the WL. That said, the rooms at the WL have just been renovated and are very nice. We found the most noticeable difference is the space in the bathroom is better at the YC than at the WL. But we really like both resorts.
The other consideration is where you will be spending a lot of time. YC is very centrally located for MGM and Epcot. WL is much better for MK. As you can tell we like both resorts. It just depends on what atmosphere/theme you prefer, etc.
I think you would be happy at both resorts. We sure have been ... having had stays at both YC and WL within the last 7 months.