You can organize your requirements quite simply to help make your decision on what sort of paper shredder to purchase.
What sort of paper will you be shredding? This involves both the type of paper and the size. If you are only shredding poor stuff, less than 100lb. stock, in single sheets, then the very cheapest will do. Ordinary letter stock in single sheets needs a bit better machine. Continuous forms, while not necessarily being of good quality paper, need a bigger feed opening. Cardboard stock, such as used for printing business cards, needs better blades. CD's or credit cards - although for most people a good pair of scissors will do for the latter - need much tougher equipment.
Will you be using the output for anything? Both strip-cut and cross-cut paper can be used for packing, but strip- cut is better for the purpose. Cross-cut is much denser - almost double strip-cut - and may not be suitable.
How much paper will you be doing? Obviously, the more you shred the heftier and faster a machine you'll need. If you're doing continuous forms, you must get a machine with a feed width greater than your maximum paper weight, or else it will be jamming continually. If you are doing enough shredding then a feeder attachment or a delivery belt or some other high-speed loader will be needed.
Will you be shredding more than paper? Will your papers contain staples, paper clips, plastic inserts, cardboard, and other stiff and/or hard matter? There are industrial- strength shredders available which can cope with even this sort of thing.
Are you handling secret and sensitive material? There are destruction standards for this sort of material and shredders built to conform with them.
Is it better to do your own shredding or to employ a service? There are shredding centrals you can go to, and there are mobile services which will come to your site. If you have occasional huge shredding jobs, and it's not overly sensitive material, it may be to your advantage to use such services rather than get equipment hefty enough for the rare big days.
Work out what your requirements will be for each of the points listed and then you'll be equipped to look into the specific makes and models.