I think it really depends on how you vacation.
The MK view may only be special once it's dark out. During the day, I'm not thrilled about seeing a parking lot. Then again, you get to watch the monorail during the day. At night, that's when the MK view will be a premium. (Fireworks and seeing the park lit up).
Lake view seems like it will be incredible in the morning and afternoon. It may also be great at night.
We're hoping to try both in December. We have a Lake view for 4 nights and are WL for 3 more nights in a MK view. In the future, I suspect we will stay lake view or standard view, unless we bring friends who haven't tried MK view.