The original broadheads and still the most popular, fixed blade heads are, as their name implies, fixed in place. That is, they have no moving parts, just static blades. They are the original broadhead design (going back to the very beginning of archery), and are still widely used today. Pros The advantages to fixed blade broadheads are:
Better Penetration - Fixed blade broadheads penetrate better than mechanical heads. For obvious reasons, this is of utmost importance! They are also less likely to break or change direction on impact with bone or deflect off a quartering animal.
Durability - Fixed blade heads are tough, rugged, and can take a great deal of abuse while remaining ready to get the job done. For this reason, they've gained a reputation for unmatched reliability. By default, anything with less moving parts is going to be more reliable in any condition.
Price - Fixed blade heads are usually cheaper than mechanical heads. While this is not an area to try and save a few bucks (after all, we're talking about the business end of your arrow), cost can always be an issue.
Cons There are two basic drawbacks to fixed blade broadheads:
Tuning - When you switch from your practice field points to fixed blade broadheads, your arrows will often fly differently and change their point of impact. This is because you're adding more surface area in the form of the blades, which can exaggerate tuning issues and problem with your bow. Fixed blade broadheads are less forgiving of a bow that is perfectly tuned.
Cutting Diameter - The smaller cutting diameter of fixed blade heads does less slicing and dicing than the larger diameter mechanical broadhead blades. This means they may not kill an animal as quickly or produce as much of a blood trail to follow.