The one in town is okay as well - bonus being close to walks and shops. Grampians Gateway (think that is what it is called) corner of road in from Ararat is pretty nice as well.
I have stayed at the one in town and as Billee says its ok and handy... http://www.hallsgapcaravanpark.com.au/ This is the only one I've used so I'm not in a position to compare with the others.