The WEEKDAY schedule (monday to Friday) for the Sheraton free shuttle bus to/from Maihama train station is awful. Just garbage. They have very few buses running between 7am and 2pm (sometimes just 1 per hour) and then after 2pm in the afternoon NOTHING. Not 1 single shuttle bus.
In comparison the nearby Hilton on weekdays (Monday to Friday) runs at least 3 shuttle buses per hour (sometimes up to 6 per hour) from 5am in the morning, all the way until midnight, every hour, without any gaps.
There are many different reasons why I found the hilton at tokyo disneyland better than the sheraton, but the fact that the sheraton has ZERO shuttle buses to/from the train station after 2pm was a big deal to me. If the 2 hotels charge more or less the same price, I wouldn't stay at the sheraton again just because of the awful weekday shuttle bus schedule.