Which weapon do you think is the most important in CS:GO?

[Heatman]

Gameplay differs from one player to another and the same thing goes with their choice and usage of weapons in playing the game. 

When it comes to playing CS:GO, which weapons do you think is the most important to carry? Some players says that it's the assault rifles while some say it's pistols and others meele weapons. 

What's your opinion on this?