In American English, only 'make a decision' is considered correct. In British English, we can use both 'make a decision' or 'take a decision', although the former is far more common. "Take a decision" is fairly unusual, but it does exist. We tend to use it when someone assumes the responsibility for making a fairly important decision in a formal context, for example "The CEO took the decision to fire the board of directors'. If I were you, I'd always use 'make a decision', because you can be sure it'll be correct. But be prepared to defend 'take a decision' if anyone tells you that it doesn't exist!

"make" is the correct term. I will make a decision when I am ready. They made their decision. I am making a decision.

make