Most Police depts and Correctional Systems choose the 870 for its durability, reliability and effectiveness.
One of mine,my HD 870 in fact, was purchased used around 1956 by my Dad. I've personally put over 3000 rounds throught it. Tight as a bank vault and reliable as a HD shotgun should be.
The Mossberg's OK, the 870s superb. Buy it, your great grandchildren will thanks you for it....