Letchworth is one of my favorites, beautiful park. NO full hookups, electric and water spigots spaced throughout the loops. 3 Dumpstations. 3 of the 8 camping loops are pet loops so if you DONT have a dog and DONT want to have one on either side then stay out of loops 1, 2 and 7. JellyStone is nice, a bit more $ but they have an awesome splashpark area, pool, and LOTS to do for kids. Its also closer to DL than Letchworth, not quite into Fingerlakes area. Skyline RV Resort is in Darien, nice big CG lots to do, pools, etc and is very close to Darien Lake Amusement Park. Owners are great, friendly and very helpful.
http://www.skylinervresort.com/