I grew up in Deer Park and the out of town guests who attended my wedding stayed at the Hampton Inn, since it is the closest hotel property to DP. *Of course, in the interest of full disclosure, I should mention that the wedding was 20 years ago, LOL.*
That said, I can't comment personally on the conditions of the rooms, but from what I can see, the reviews on TripAdvisor, Travelocity and Expedia are decent, giving it 3 out of 5 stars. Not spectacular, but not a dump, either. I can tell you that the hotel is in an area that I am very familiar with and consider to be quite safe. The hotel itself is just off exit 52 (Commack Road) of the Long Island Expressway, so it's convenient in that you won't have to navigate all sorts of ancillary roads to find it. The property is across the street from a residential area and adjacent to a large shopping area that contains stores such as Costco, Target, Marshalls, Home Goods, Wal-Mart and Kohls. There is also a Starbucks and a diner within the immediate area, as well.
I'm not sure where your gymnastics meet is, but from the street the hotel sits on - Commack Road - it's a straight shot to Deer Park, about 4 miles south. *There's also a Tanger Outlet Center located on this same road, in Deer Park, in case you have some down time. There are restaurants and a movie theater in the complex, as well as the shops.*
The other hotels mentioned - the Marriott and the Hilton - are also nice properties, located along a more commercial route that is dotted with lots of businesses and retail stores. It's a little bit further away (about 8 miles west of Deer Park, at Exit 49 of the Long Island Expressway), but would only add about 10 minutes to your travel time. Their ratings are also in the 3-star range, and their room prices are about $30 more per night...although I did see a special on Expedia for the Marriott that includes breakfast for 2 in the price. Definitely food for thought!
If you need any more specific information about the area or directions, I'd be happy to help.