nibblers or three jaw shears, Harbor freight sells them cheaply.
Better brands are better. They cut nice and quiet and leave a clean edge that's not as sharp as most other cutters.
Very little mess or noise.
Harbor Freight Tools - Quality Tools at the Lowest Prices
You can also pick up an attachment that works with a standard 1/2 inch drill motor.
they have three jaws and cut so the only real 'waste' is a narrow strip of metal that curls up nicely so you don't have to hunt down 10,000000 little half moon razor blades.
For aluminum, it helps if you put some dish soap along the cut line to keep the blades lubed up.