Paper cutters are pretty cool. There's nothing like feeling the power of an inlaid-steel blade plowing through a thick lift of stock. Paper cutting machines fall into a few basic categories relating to their drive system. Within those categories the width of the blade is the largest factor. The major categories of paper cutter are hydraulic, guillotine, electric drive, and manual drive. Hydraulic or guillotine cutters are very heavy duty and are used in heavy production environments where deadlines are tight and throughput is everything. This category of cutter is rather broad and there is a lot of variety so make sure you do some research before you commit to a specific paper cutting machine.
A common rule of thumb relating to cut width is that you want to be able to spin your largest sheet size under the blade. For example if your max sheet size was 12 x 18 inches, with a corner to corner measurement of 21.6, would mean your cut width should be larger than 22. This rule helps to ease operator workload and ensure that you're within the load rating of the cutter.
Electric paper cutters are generally mid-range and are expected to be used every day or several times a week. They are quite fast to operate but cannot handle thick lifts and their cut width generally maxes out around 23 inches.