Stay at the W. Of all the SPG hotels, you will get there the fastest on the airport express. Should not be a problem with infant. Seen it done many times. There are seats on the airport express as well as luggage racks near the doors.

Sheraton involves a shuttle transfer. LM is quiet and peaceful but way too far.

There is a large mall under the W that can seem daunting to navigate once you get out of the airport express station. Look at the hotel specific thread and some folks have given good tips how to get to the W quickly. Not a problem. There is also a large grocery store (360) right in the mall for ready-made food, supplies, drinks, etc.

W rooms also tend to be a little bigger than Sheraton. Maybe if you need space for baby stuff sprawl.