I have an idea - split your stay 1/2 and 1/2. Try them both.
If you don't want to do that, I would pick based on how much time I was planning to spend at MK. If the answer is A LOT, then I would choose WL for the sheer convenience alone. I would also consider which theme is the most appealing to me. Both resorts are very well themed. I also would take the rate into consideration. Of course, if they are the same that blows that theory.
PamNC