Happy 4th. to all! I'm just about ready to upgrade to a bigger mower for my business. I live in Pittsburgh, and we've got hills. Most of my customers are residences that sit on a quarter acre. There are large flat portions but there are tricky hills in spots. Here's the question: Should I get a toro ztr and finish with a 21" self propel or should I get a 36" walk behind? Currently I use a 21" lawn-boy for twenty three customers. Smallest lawn is 1/8 acre, largest is 1 acre. My legs are taking a beating. Thanks for the help. HERE'S TO THE STARS AND BARS! THE COLORS THAT NEVER RUN!