I've stayed at both BWV and OKW multiple times. I've gotten BWV SV villas (studios and 1-BRs) at 6-7 months out, multiple times--including in August.
I love OKW...I love strolling the grounds; love the pools (feature and neighborhood)...great gift shop...counter service is decent food, but not great for "sitting and eating"...Olivia's (sit-down restaurant) is wonderful. The boat rides, as someone else noted, are wonderful, too...The CMs at OKW have been unfailingly friendly and helpful...it's great to be able to walk to Downtown Disney, or over to Saratoga Springs...and OKW's central location makes bus rides to any of the parks relatively short.
BWV is my least favorite
DVC resort (keep in mind I love them all...just love the others more than BWV)...I've encountered unfriendly, non-helpful CMs at BWV more than any other Disney resort...that leaves a bit of a 'bad taste' for it...but there are still more friendly/helpful than unfriendly/unhelpful CMs at BWV...it's a nice resort, w/great grounds and entertainment options all around it...and it's sure nice to be able to walk to Epcot and Hollywood Studios! Their boat rides are nice, too...
As for the villas themselves--OKW's "win" on that score, hands-down--so much roomier and private-feeling! But generally, I find most DVC villas "feel" the same (w/different colors/patterns, depending on resort), w/the exception of OKW which is significantly bigger/different-feeling...
Either will make for an altogether grand vacation...if it were me doing the choosing, I'd base the decision (assuming availability) on the amount of time I think I'd be spending at Epcot/HS vs Downtown Disney...
Have fun!