For automotive rubber hoses and nylon lines, I prefer a hose cutter that uses a pointed tip to start the cut, like the NAPA SER 774033 (UNSPSC 27111513).
It doesn't flatten the hose as much while it cuts it, which results in a more square cut. Unfortunately, it is very hard to find hose cutters with this pointed blade. Another source is home brewing equipment suppliers - they have a tubing cutter that also has a pointed blade and cast-alloy handles (the NAPA one listed above has glass-filled nylon handles).