I have done both so here is my take from a family of 5...
BLT:
This is my favorite, not the wife or kids, but mine! I like the styling and the relative 'newness' to it. I love the location right by MK and the ability to walk too and from it is worth the money and then some! No rushing at the end of the evening to get inline for the monorail, no pushing and mad dash for the boats, no jostling for position like sardines to get on the right bus etc... Just casually walk on by! Loooooooooove it ;o) Being able to use the walkway directly over to the Contemporary is also a big bonus, you get to use all the awesome facilities and amenities there too so its a nice trade off.
However, the pool isn't the greatest and there is very little to no 'theming' for the kids. The lobby is nice and plush, but it looks just like an upmarket hotel anywhere. Despite it being relatively 'new' and modern, it is showing its age in spots and we could definitely see the 'wear and tear' in our room.
That said, I really enjoyed it but thought it was overpriced for what it was. You can get a similar experience with respect to walking to MK and the CR amenities by actually staying at the CR!!
WLV:
This is my wife and my kids favorite location. The location reminds my kids of home (PNW Cabin style!) and it has a much better 'feel' to it regarding Disney theming, the huge impressive entrance hall, the food options etc... It is more of a 'complete' hotel as opposed to an annex to the CR like the BLT often feels. The pool is awesome! My kids love it, and with the new bar and grill poolside it will be even better! With a family of 5, 2 of them in a double stroller we were concerned about having to consistently fold the stroller up to get the kids on the bus or the boat. We ended up using the boat almost exclusively. We were served by one of the larger boats almost every night and as such we were able to keep the stroller up and lock it down by the side of the boat. This was a huge plus. The boat ride was quick and was also very fun for the kids!
The 1 bedroom villa was really nice, a separate shower and toilet with an additional sink and bath tub in the bedroom made it easy for everyone to take care of business. The kitchen was great, full sized fridge and stove, complete with kettle, toaster, microwave etc... all the things you need. They also have a really cool Pizza delivery service that runs up to midnight! It's pretty darn good too! The washer and dryer was also essential for a family of 5 on an extended stay. All in all the space was great, the additional pull out queen sofa bed was a god send and we thoroughly enjoyed our stay there, So much so that we tried to book it again this last time but couldn't get the availability.
Conclusion:
If I had to choose between the two? I'd definitely go with WL, simply due to the level of enjoyment my family got out of it, in an ideal world I would do a split stay and have the best of both worlds! But if not and there was only one? I'd do WL due to all of the things stated above. However, to throw a wrench in the works, if a great discount comes out and you can get a room at the contemporary resort for really cheap then i'd do a hybrid and get that! lol..... ahhh good old choices ;o)
Whatever you choose you will have a great time regardless.