The printing and copying functions are rated in pages per minute (ppm). Although reality never meets the exaggerated claims look for 10 ppm for a simple black text document. Color speed depends on resolution and ink coverage and can vary widely. Scanning speed is not as widely provided by the manufacturer but a rule of thumb is the faster the printer, the faster the scanner.
Cost to use
With an inkjet device your main expense is the ink. Since the bulk of your work will include black, look for a model with a separate black cartridge. For a laser device, compare toner cartridge yield found on the cartridge packaging. Expect 2,500 copies for black for a basic text document. Make sure your device will run with your basic white copier paper, rather than heavier or special paper that is more costly.
Here you need to be concerned about both the printer's and the scanner's resolution. Print resolution is measured in dpi or dots per inch, and a 600 by 600 horizontal and vertical dpi is the minimum. Look for the optical resolution on the scanner, and go with at least 200 dpi for a printed page, higher for photo scanning.
Look for a control panel that is intuitive and easy to use. The LCD panel should tell you clearly what is happening. The keypad should mimic a traditional fax interface and include a large copy button for that quick copy job. A multifunction peripheral needs a paper handler for printing and incoming faxes as well as a page feeder and output tray for faxing and copying. Look for at least a 100 page capacity for each or you will be constantly running to refill.
Some nice features to consider are the ability to enlarge or reduce the size of the copy, printing up to 100 copies at a time, or for single copies, a one touch button.
The computer interface between a multifunction device and you needs to be intuitive and easy to use and understand. Make sure you see the machine in operation and can try it out before you buy. If it is too complicated, you will be discouraged from using one or two of the functions, which is the reason you are going multifunction in the first place. Manufacturers will often bundle in special software to enhance your output, including software to design cards and marketing material, and to doctor photos and remove the dreaded "red-eye".