Let me preface that I am neither an attorney nor financial planner. The opinion which follows is merely that- an opinion, not advice.
Why choose only one? Diversification has long been touted as an important key to any successful portfolio. There appears to be no apparent harm to possessing physical bullion; however, many authorities believe that owning paper receipts for bullion held by depositories carries the potential for enormous risk. Physical gold and silver have been considered symbols of wealth for millennia and hedges against inflation for centuries. Banknotes often bring the owner pleasure when viewed...a pleasure few derive from bullion assets.
When it comes to a financial return: win, lose, or draw, if the journey carries the pride of ownership, crunching numbers matters less.