Greenlee punches are really good for making holes in sheet metal that's
too small, flexible, fragile or inaccessible to drill, but they are
fairly expensive. Otherwise use a less-grabby step drill (Unibit, etc)
or drill a small hole and enlarge it by hand with a tapered reamer like
this one:

www.dansdata.com/ images/tools/reamer500.jpg

Jim Wilkins