How Fast Should I Lift Weights?

The two different style of lifting speeds you mention each have their positives and negatives. Both fast and slow reps can be good and it is always wise to mix the speed up regularly.

When you lift fast, you should be moving the bar as quickly as you can without losing tension in the muscle. The heavier the weight, the slower the bar will go regardless of how fast you are trying to move it. The major downside of lifting fast is that sometimes too much momentum can come into play in an exercise This can reduce the tension in the muscle and decrease the benefits you get from it.

The theory behind slow training is that it removes all momentum from the exercise, keeping all the tension on the muscles. This is very true. There are several downsides to slow training. The first is that you won't be able to use as much weight on the lift. Second, slow training is not well suited to certain exercises such as power cleans, which rely a lot on momentum. Third, in real-world athletics, there are very few sports that use slow movements. Using slow training will not prepare you for those sports.

As far as lifting pace goes, do both. Try alternating pace with each lifting day, e.g. fast one day the...