Choosing the right blade for your circular saw can make all the difference in the quality of cuts you can make and the life of the blade. The following types of blades can be used in handheld circular saws and table saws (except for dado blades which are for table saws only)
Ripping Blades - saw blades for cutting along the grain.
Cross Cutting Blades - Have teeth specifically designed for cutting wood across the grain.
Combination Blades / All Purpose - can cut both along and across the grain of wood, but the quality of the cut will not be as high as with a blade made specifically for the task.
Planer Blades - have deep slots between groups of teeth to make a smooth cut and reduce the need for sanding. Planer blades are usually all-purpose blades, able to rip and cross cut.
Plywood / Veneer - have very small teeth, they are ideal for cutting through thin wood and plastics.
Aluminum / Plastic - have medium size triangle teeth for cutting through plastics as well as non-ferrous metals such as aluminum, brass, and copper.
Metal Cutting - have groups of smaller teeth separated by slots ideal for thin pieces of mild steel (usually up to 1/8 inch / 11 gauge).
Dado Blades - can be used to cut slots in wood (for table saws only).
Size - The most common size is 7 ¼, but blades are also available in 3 3/8, 5 ½, 6 ½, 8, 9,10, 12, 14 inches as well.
Teeth Material - The material the teeth are made out of determines the quality and how long the blade will stay sharp. Steel teeth are the least expensive, high carbon steel are a little more expensive and higher quality, and carbide tips are the most expensive and most durable.
How to Choose
Determine the size of blade you will need. When cutting through material thicker than the depth of your saw, it is best to make the first cut through slightly more than half of the thickness, then turn the material over to complete the cut.
Choose a blade type based on the material you will cut and the trade off you want to make between changing blades and cut quality. Another way to get the best cuts without changing blades is to buy additional circular saws (e.g. have one saw for cutting wood and one for vinyl, etc).
Determine how much use you will get out of the blades. If you are an occasional user, a steel blade will do fine. If you are a heavy user with big jobs, a carbide tip blade is the way to go.