Which tool do you use to crop a human portrait from an image and how ?

in photoshop the pen tool is best to perform this, bcz it meet curves & straight lines at the same time,

If the background behind the human portrait is a solid color or even a color mix distinguishable from the human portrait hair ,face and shoulders. i recommend you use the quick selection tool and click+drag. which is the easiest way to it.

Don't use the magnetic lasso, magic wand tool or similar hard-to-grab tools.

If you are a professional and you want the best way to do it. You must go with the Pen tool. which is the hard way but perfect way to do it. 

There are couple of tool you can us , Pen Tool , Lasso Tool , or for quick edit try Magnetic Lasoo Tool which auto follow the outline you selected

We can crop a human portait easily by using a Pen Tool.