It's not an easy question to answer. At the end of the day, you want the flag to look great on the flagpole. In heavy winter weather, flags break down quickly. There are more options than you might think. Well go through those options here...
Fly Polyester Lock-Stitched
The standard fabric, Nylon, does not cut it in winter areas. Nylon fabric is lightweight and flies in the slightest breeze, but will fall apart in heavy winter. Polyester is about twice the weight and designed for durability against these conditions. For Standard Polyester Flags, click here.
Fly smaller flags Flying one size smaller will increase flag life. The smaller the flag, the less fabric area to catch on the wind and elements. For Standard Nylon American Flags, click here.
In addition to polyester, smaller flags, you can also have the flags reinforced. Reinforced flags have vertical stitching off the fly-end. There are also reinforced corners. All of this is designed to prevent fray. For Polyester Reinforced American Flags, click here.