We stayed a couple years ago at the Residence Inn in maybe Harrisburg?. It's pretty close - no need for GPS to find your way. We came in from Niagara Falls in the afternoon, did the Hershey quick tour, and then spent the next day enjoying the rest of Hershey. Can't remember if they had a pool, or if it was heated. Clean place. The hotel leaves Hershey kisses in your room. This was mid-July & I made my rewards reservation the night before (in Niagara).
There are no full service Marriotts near Hershey Park. I have stayed at the Courtyard Harrisburg Hershey several times. It is pretty new and very nice. However, you may prefer to be closer, which would limit your choice to the Springhill Suites.
We went last year and had a great time...couldn't get into the Marriott since we had nothing booked prior to getting there and ended up at an expensive "dive" hotel that I wasn't too crazy about. One recommendation is to purchase your park tickets from one of the local grocery stores for discounted rates. Our hotel sold discounted tickets, but we asked at some local gas stations and they directed us to the local grocery store for cheaper tickets.
We stayed at the Springhill Suites in Hershey last summer with our 2 elementary school aged kids and visited Hershey Park. The staff was very helpful and friendly. We arrived after midnight due to flight delays, and they had the keys ready and waiting for us. The hotel doesn't have a lot of frills, but it is convenient, offers a hot breakfast, and has microwave oven and mini-fridge in the room. They also have a mini-market in the lobby for snacks, drinks, etc. They are claiming to have free high-speed internet access in the rooms now, too.
The Spring Hill suites that some others mentioned in great ---literally less than a mile from the park - new - clean - full of other families too ---plus the mini store in the lobby was great and the continetal breakfast was much better than the standard muffins and OJ. Finally- right next door is an antique car museum that is great for the car buff of the family. Plus plus- the route to the park from the hotel helps you avoid miles of traffic trying to get to the park from Rt 39