Choosing a Singleton or a Category?

Question

Fairly early on in my app, when I was a lot less experienced than I am now, I wanted to spice up some transitions between view controllers with my own custom animations. Having no idea where to start, I looked around SO for a pattern like MVC that could be accessed from nearly any controller at any time, and as it turns out, a singleton was the way to go.

What I didn't realize is that there seems to be a strong and well-defended hatred of the singleton pattern, and I myself am starting to see why, but that is beside the point.

So, a while later, I decided to move my very same implementation into a category on UINavigationController (after all, it handles transitions!), kept the original classes around for comparison, and am wondering which method would work best. Having thoroughly tested both implementations, I can say without a doubt that they are equal in every way, including speed, accuracy, smoothness, frame-rate, memory usage, etc. so which one is 'better' in the sense of overall maintainability?

EDIT: after reading the well-written arguments you all have made, I have decided to use a singleton. @JustinXXVII has made the most convincing argument (IMHO), although I consider every answer here equally worthy of merit. Thank you all for your opinions, I have upvoted all answers in the question.

Answer 1

I believe the best option is use the category.

Because if you are already using UINavigationController, do not make sense create a new class that will only manage the transition, like you told: (after all, it handles transitions!)

This will be a better option to maintain your code, and you will be sure that the thing do what they expect to do, and if you already have an instance that do the transitions, why create another?

The design patterns, like singleton, factory, and others, need to be used with responsibility. In your case, I do not see why use a singleton, you use it only to no instantiate new objects, you do not really need to have only one instance of it, but you do it because you want only one.