My 7 year old is on the spectrum and I have a 4 year old. This past April we did the Eastern and it worked out well. My Spectrum kiddo wanted to go back to the ship by noon each day so we actually found the more at sea days was a bonus for us. We did a beach day in Tortola and a private charter boat in St. Thomas. She was over the charter boat by about 11:30am but she loved the beach day. Overall she was much more at home on the ship and getting into the cruising routine. of club in the morning, lunch, swimming, activity, dinner prep, dinner, show... Either itineraries both will work for you! Have fun!
ETA: we were on the Magic and hung out in the kiddo pool section so the crowds weren't that bad on sea days... they would be much worse probably on the bigger ships so I can see why others are saying go on the Western so you'd have the ship to yourself