Hi, Ruby. Today, I would go with a steel or fiberglass door. They are really well built and require minimal upkeep. You can choose to paint or apply a wood faux finish and it will last many years. Wood doors require a lot more attention. As far as insulation goes, the fiberglass ones are now superior in my opinion, with metal second. One of the issues is how much glass you choose for your door design. One sheet of glass is not a very good insulator so you will want to limit the amount of glass if this is an issue. A good metal door with a small amount of glass would be my choice. These are relative inexpensive but I would not buy the cheapest. Look for a combination of thicker steel and better insulation than the cheapest available. Don't forget to insulate around the door when you replace the old one and the voids outside the door frame are readily available for this.