Hilton is closer to the park and easier to come/go. Parking is very pricey and the service is nothing special.
I haven't stayed at the Sheraton in many years, but it had much better service.
In spite of the service being better at Sheraton, I stay at Hilton because it's so easy/close to the park. It's a a steep hill to get to the parks. Hilton is almost across the street - maybe a one block walk. While the Sheraton isn't much further, the hill is steep enough that it can make a difference depending on the mobility of your group.