Depends entirely on your personal preference.
But the same way most people will recommend that you not give in to "1 of each" collectoritis in terms of plant selection, many folks also will say a smaller number of grouped fish is more aesthetically pleasing than 1 of each.
Tetras of similar size will often school together. For example, your black and regular neons. One benefit of a uniform school is that the eye treats it as a single entity, instead of seeking out differences.
My personal preference is to stick with 1 or at most 2 types of similar fish in a single aquarium. For example, in my 30 I have only glow-lite tetras (plus otos and blue rams). In my 55 I have 2:1 serpae and red-eyes. In the past, when I have had more than 2 species of a similar fish in a single tank, I have regretted it.