Cutting sheet metal

I am looking to purchase air nibbler or air shears. I would like some comments on the pro's and con's of each tool. I would rather not buy both. I believe the air nibbler can make tighter turns...why would I need air shears?
From what I have read they will both cut metal up to 18 gauge. My pair of hand shears bends flat sheet metal...do air shears do the same?

 

[MONMIX]

I always use a " wiz-wheel " to cut sheet metal. A 1/8th wheel will give you a closer tolerance than a nibbeler.

I have never actually used shears.

There is an air-hammer bit that works well too but takes more controll.