Running a little stump grinder is slow, but relatively easy work. Most rental companies have them readily available. Last one I rented was a Toro based on the mini skid steer platform. I liked everything about it save it was gas powered and lacked the power to make fast cuts. They won't rent diesel powered grinders as they said they had a lot of issues with customers putting gas in them. Can't blame them really.
If you have time on your hands, Epsom salt and a big drill bit will expedite the stump rotting. We took 6 tulip poplars down right after we moved into our place. I couldn't get a grinder into one of the stumps and a friend suggested the drilling holes and Epsom salt trick. Took a few years, but the stump eventually rotted down below grade.
