A great aspect about compound bows is that you can hold them at full draw. This feat can only be accomplished by the cam system that is on the bow. The term for this is called let-off. The design of the cams have a great effect on the amount of let-off that a bow has and the let-off typically ranges from 65%-85%. What this means is that once the cams have turned to a certain point, there will be a 65%-85% let-off in the weight that you are holding. If you had a bow with a hundred pound draw weight and an 85% let-off, then you would only be holding 15 pounds of that weight at full draw.
Compound bows have gained their popularity because of the amount of stored energy that they are capable of producing. When you talk about stored energy, more energy means more velocity. When you are using a cam system to propel your arrow you can slightly manipulate the drawstroke so that you can reach the peak weight more quickly. Various different cam systems are out there from which to choose. You can choose from single, hybrid, binary, and twin cams.
Single cams come equipped with an elliptical shaped cam on the bottom of the bow and a round cam on the top. These bows are much quieter than conventional twin cam systems. They are also easier to maintain. This is because there is no need for the compound bows cams to be in synchronization. You can get single cam bows that are aggressive or you can get a single cam that is much smoother. Single Cams offer the shooter reliability and a good stop at full draw. It is for this reason that they are still a popular choice on the market today.
Hybrid Cam systems have two unevenly elliptical cams. They are valued because they do not have some of the synchronization issues that their twin-cam brothers might have (which we will talk about later) due to their asymmetric design. They are great if you want a speedy shot that is not too loud. If you were looking for something that has a little more mph, then I would look into getting the twin cams, which are perfectly symmetrical. Either they are both round or they both have elliptical cams on each side of the bow. They offer the shooter great speeds and excellent accuracy, but they do tend to have a slight maintenance issue. This is not to say that they will break down, but they do require a little bit more TLC to maintain their prestige.
Keep in mind that not every bow is built the same. There will always be trade-offs between speed and noise, and there will always be a difference between wheel cam, soft cam, and hard cam. The round wheel cam is typically going to offer the shooter a smoother shot, but they will not be able to store as much energy. Soft cam will get you more speed, but they will be less forgiving. The hard cam will give you that blistering speed you have been looking for, but will not get even the slightest forgiveness. Stay true to your shot and practice. If you do that, any one of these compound bows can be just as good as the other.