I voted 20 and 21 inch, because those were the two smallest choices in the poll. In fact, I can get by with smaller deck sizes on my 6500 sq ft spread and really like a tiny 14 inch deck electric mower to get into tight spaces. Currently, I have mowers with blade lengths of 13", 14", 15.5", 2 X 10", 20" and 21", but would be fine just keeping the ones with the 13" and 2 X 10" (twin) blades. All of them are push walk behinds.