Studios are also the most popular room type. Depends on how important staying in the Epcot area is to you. If you'll be happy at SSR, and want to stay at BCV/BWV once in a while, buy SSR. If you want to stay at BWV/BCV and will be disappointed if you don't - or stressed out if you end up waitlisting, buy there.
If you can't plan more than seven months ahead, it doesn't make any difference where you buy.