For my opinion, read on. This is a series notes based on questions that I have been asked by people considering the purchase of a microprocessor training or development system, generally for home or hobby use.
People designing or working with microcontrollers each have their own favorites.
It's a bit like asking which is the best car. There is no one best. Each is possibly better suited to some specific task, but will also handle many other tasks with little difficulty. I'm sure there are people who will disagree with some of the points below. Please let know what you disagree with and why, or what you agree with.