I would have chosen lion as our nation's symbol. Lion can represent multitude of things such as strength, justice, fearlessness, and power! All of these were part of the US when colonies first united and fought against british. Lion also resembles a great military might and US has this even to this day and had this during old times as well as evident by our win against the notorious british regime.
Having a lioness to be part of country's symbol also resembles being caretakers as a great mother providing protection. US has mostly been a safe refuge for people seeking the protection of its warmth and security. The colonists came to US mainland (although not orginally called US) for better life thus lioness or lion are great symbols.
