I have stayed several times at both hotels and you can't go wrong at either.
At the Boardwalk you have access to 2 parks, a short walk or boats to Epcot, and the boats to MGM.
At the Contemporary you have access to 2 parks, either a short walk or monorail to the Magic Kingdom, and the monorial to Epcot.
Which parks do you and your husband like the most? I would let that decide which resort to stay at. At 9 months old, your baby is not going to be picky about which park she is going to. Strollers are available at all the parks. If you want to bring your own stroller, you can bring your own strollers on board both the monorial and the boat transportation by the Boardwalk. The only drawback would be getting onto the buses, as the stroller would have to be emptied out and closed up.
The Contemporary has nice big rooms, it DOES have theming, just not as much as other Disney hotels. It has a sparce/space/future theming and this either works for some people or it doesn't (that said it is my favorite on the monorial system). It has easy access to the monorial, great restaurants, nice big pools, water sports available and easy transportation to the other hotels for dining. There is no drawback staying here.
The Boardwalk.....I dont know which kind of room you got a rate on, as the rooms vary greatly. But the theming is beautiful, there are nice pools, great places to eat, access to the Yaght and Beach Clubs, easy walk to the Swan and Dolphin. The Villas are great for families with small children because of the washer and dryers available. I love the Villas for this reason alone and have stayed there often when my kids were young. The only problem I had with the Villas was if my room was facing the Boardwalk itself, there were noise problems, especially late at night, but this was a problem on the Villas side, where the lounges were open late at night.
I think either choice you make, you will be happy. You didn't say how long your trip was, but you could also consider spliting your trip between the two hotels also. Hope this info helps. If you have any further questions, send me and email and I would be happy to help further.