This 2 piece slipcover has worked the best for my sofa than any other that I have bought.  It fits over my 2 large box cushions better than the 3 piece.  It washes well and is great for my pets.
The reason for 4 stars it does become slightly untucked and has to be tucked in after frequent use.  I have not been able to find a slipcover that will stay tucked.