No matter how much attention you pay on your oral hygiene, an errant cavity can still manage to sneak through occasionally. The sooner you realize the unthinkable has happened, the quicker you can take care of it. Quick action will better the chances that it will not reoccur or affect your neighboring teeth. However, once your dentist removes the decayed part of your tooth they will need to fill it with something, what that is, is up to you.
The most commonly used types of fillings are gold, silver or amalgam, and composite resin. Depending of your own priorities, each of them have their advantages and disadvantages. Gold fillings do not erode, so they can last for at least 10 years and in a lot of cases a lot longer. They are strong, and give you a very strong and durable bite. However, they are more expensive and require more than one visit to your dentist. Also depending on your taste, they can also be less than aesthetically pleasing.
Silver fillings or amalgams also have a good lifespan of 10 to 15 years, and while not as strong as gold, they are very effective. The advantage is that they are also less expensive than both gold and composite fillings. However, they do not match the color of your teeth and can be distracting. They also require more work to put in place and can create a grayish hue to the tooth over time.
The main advantage of composites is their color. It can be very closely matched to the actual color of your teeth and is very versatile. Composites can be used to fix fractures and cracks, and even repair worn teeth. Unlike amalgam, it does not need as much preparatory work on your tooth but it is not as durable as your other options, and will require additional dentist visits.
Your choice will entirely depend on your needs and your priorities. Make sure to talk to your dentist before deciding. Their experience will provide you with all of your options and can help guide you to the best solution.