Confetti-cut shredders, or cross-cut shredders, cut the paper bot horizontally and vertically, making very small fragments.
If you're purchasing a very large shredder, the lid and shred mechanism may be heavy or cumbersome, so look for a side-loading or slide-out basket rather than a unit where you have to lift the top off to empty it.
Many people underestimate the amount of paper they think they will shred. It is better to buy a shredder that is a bit too large than to pay high maintenance fees for a shredder that is too small and, therefore, overworked.