I've rented grinders and have been happy with them. Except...let the stumps get dry before you do it. I tried to take out some poplar stumps that were too green and the grinder choked on them. The didn't chip, they sort of wadded and the pieces wouldn't tear loose. The trees were dormant but still had too much water in the trunks.
The rental place here even asks you how long it has been since the tree was cut.
