Sleeping Bag Temperature Ratings
To find the best sleeping bag you'll first want to know what temperatures you expect to be sleeping in. Most sleeping bags are classified by season. A 1-season bag or summer sleeping bag is typically going to be comfortable in temperatures of 40 degrees Fahrenheit or higher. A 3-season bag typically will keep you comfortable in +15 to +40 degree temperatures. If you plan to do some winter camping you'll need a 4-season sleeping bag which will keep you warm in temperatures of -10 degrees Fahrenheit to +10 degrees.
Most sleeping bag manufacturers will give a temperature rating. Choose the sleeping bag rated to the temperatures you expect to be camping in. Remember, you can add a sleeping bag liner and more layers of clothing for colder nights but start with the bag that will provide the right amount of warmth. More information on temperature ratings is available here: Sleeping Bag Buying Guide
Sleeping Bag Insulation
When you buy a new sleeping bag you'll have to choose between down or synthetic insulation. Both types of sleeping bag insulation have advantages. Down provides the best warmth-to-weight ratio. A down sleeping bag, just like a down jacket, will be lighter and more packable than a synthetic of the same temperature rating. However, down doesn't provide warmth when it's wet. Therefore, synthetic is a better insulation choice if you camp in wet conditions.
In recent years, the technology of both down and synthetics have improved. Many outdoor brands are now making sleeping bags with water resistant down and strides have been made to make some synthetics act more like down. Watch this video to learn more about the difference between down and synthetic or read this post: Down vs. Synthetic Insulation.
If you are looking at a down sleeping bag, it's also important to understand Down Fill Power.
Sleeping Bag Style
Sleeping bags come in many different shapes. A mummy style bag fits tighter around your body to keep you warm on colder nights. Rectangular sleeping bags are more comfortable for people who move around a lot throughout the night but they aren't as warm and they're heavier to carry. Also, most sleeping bags will come in a regular and long size. It differs with the sleeping bag manufacturer but in general if you are over six foot tall, you'll want to select a long sleeping bag.
Find more information about sleeping bag style and fit here: Sleeping Bag Buying Guide.
For more information on choosing the right sleeping bag, check out one of these articles:
Sleeping Bag Buying Guide
How to Wash a Down Sleeping Bag
Down Vs. Synthetic Insulation
The Gear Doctors Guide to Sleeping Bags
Winter Camping Tips
Deals on Sleeping Bags