Gold, of course, is much more valuable. If you had to, you could grab a handful of gold coins, travel to many parts of the world, and live for months or years on the proceeds. It’s held by (in increasing amounts) by central banks all around the world.
In addition to its beauty, it is extremely malleable, will never tarnish, and conducts electricity extremely well.
Silver has some special qualities going for it as well. First, it has lots of industrial uses. Second, it has tremendous antibacterial properties. Much of the silver mined each year is a byproduct of mining for another metal. That means that if the demand for copper drops, we can expect less new silver to be brought to market. Finally, most silver is used up and is unrecoverable with current prices and technologies.
In addition, it’s much less valuable than gold. That’s an advantage if we experience a currency collapse, or simply inflation great enough to make people prefer hard (gold or silver) money. In that type of situation, would you rather pay for gasoline, food, or medicine with a few silver coins, or pay with an ounce of gold and get your change in dollars?
A more thoughtful way to consider this might be, "Given X dollars to invest in gold/silver, how much should be allocated to each, given my particular circumstances?"