In general the larger the monitor the better. Unfortunately realestate is usually a premium at the front desk. You should never use a monitor that is less than 15 inches.

Flat screen monitors are very popular and take a lot less room.

There is a trend for wide screen monitors. While these are great for watching DVD movies, they are not generally not a plus at a front desk as they are wider than they need to be.

AutoClerk supports touch screens. If you wish to install a touch screen, get one that uses a USB interface. Don't forget your computer will need a USB port dedicated to your touch screen.