It's hard to recommend a situation where Singleton is the best choice. Singleton should only be used where its benefits (it allows client code to pretend to create multiple instances but secretly enforces a limit on number of instances, and provides a globally visible access point to do so) outweigh its many limitations (it's hard to test, inflexible and hard to dynamically configure, spreads the knowledge that it is a Singleton throughout the code, and embeds a potentially volatile business decision deep into the structure of the code.)
For these reasons, a lot of people here would recommend that the Singleton pattern should hardly ever be used. Almost all occasions where a Singleton might seem a reasonable choice would likely be better served by "just create one" and pass it around as needed.
To elaborate on what Frank wrote, even when we only want to have one instance of a class in a system, what we still typically don't want is
- having that class know that there only exists one instance in the system
- having all clients of the class know where the instance they should use is originally coming from.
I've come to the conclusion that actually *most* uses of the Singleton patterns are misuses. In the system I'm working on - which is under development for nearly a decade now and consists of roughly a million lines of code - there are only two places where we used something "singleton-like" and it didn't hurt us: we have a global access point for getting a logger, and we have a global access point to determine whether the system is running in development- or production-mode (the latter makes it possible to disable non-production-ready features in production-mode).
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus