Happy 40th!!! I had a similar choice last year for my 50th. I wanted to treat myself and stay at a deluxe. I chose the Contemporary. For me, what I did was looked online at the pictures of the rooms and based on my instinct, picked what felt right for me. Now with that being said, each of the resorts you mention all have benefits and would be a wonderful place to stay. The other thing to possibly consider is where you plan to spend most of your time. If you will be mostly at the Magic Kingdom, then maybe the GF or WL. But if Epcot or Hollywood Studios is your preference, then maybe pick the Boardwalk. But ultimately pick what will make you the happiest and make your birthday that more magical!