The greatest difference between Grendel's "home" and Heorot, as depicted in Beowulf, lies in the existence or absence of light. In Grendel's lair, light fails to exist. The moors are filled with other monsters and "dire breeds." It seems to be a place of depression, sadness, and hatred. Heorot, on the other hand, is a place which celebrates God and "lives" in God's light. The people of Heorot sing and praise God daily (unlike Grendel who curses him).
Heorot was built for the celebrating of God and the bounty God has bestowed upon Hrothgar. The moors, on the other hand, exist as a place where the exiled and forgotten go.In the moors live monsters, ogres, elves, and phantoms--those beings which are not welcomed by God. God is not present in the moors.
In essence, Grendel's home represents the evil in the world, and Heorot represents the good in the world.