I personally think that both slow reps and fast reps work, In a real sense you have to develop a feel or experience to arrive at a style that works for you. There is a ideal groove (combination of rep speed, range of motion, etc.) that every weight lifter will develop with experience over time. It takes time.
Two examples of diverse rep grooves are two of the best Mr. O's, Dorian's and Ronnie's styles. Yates generally used a full range of motion, and explosive raising phase, sometimes a pause and then a slow negative. Coleman, a rapid explosive, rythmic, partial rep style. Both methods produce results thats obvious.
The bottom line is that both methods work, both methods produces results, and both have their pros and cons. Obviously these methods have enough in common to produce outstanding results.
On a related note,
I personally train predominantly with partial, explosive reps with great overall effect in muscle and strength. I also make use of full range reps done slower when I feel the need. If I had to choose though I would pick explosive partials for more producing more overall result in mass and strength. I feel this way despite being a fan of Dorians style and being trained by him a few times.