If a computer is likely to be stationary at the office, we recommend going for a Desktop or Mini-tower. An equally powerful laptop is usually about 30-35% ore expensive than a desktop or mini-tower computer, but if mobility is needed, then the laptop is the way to go. Excluding accidental damage that can happen to laptops from being carried around, we also see failures of hardware components much sooner. Between the desktop and the mini-tower, our experience is that the mini-towers have the longest lifespan so if you have the room and don't mind the larger box then we say, go for the mini-tower.
Sometimes our newer clients have said they can find a lower price on a computer and ask why we are not recommending the cheapest. Our response is that most of the advertisements from the major retailors and computer vendors are showcasing their best-priced computers. Like all machines advertised for price, these computers have low-end processing power. That reduces the usable life so we always recommend something a bit more powerful, but without paying for resources that you'll never use. It should also be noted that these lower priced computers usually have the Home version of the operating system instead of the Professional version which provides the networking capabilities typically needed in business.
A stationary office computer is often called a desktop, but there are really four basic kinds; the Mini-tower (usually sits under the desk), a Desktop (under the desk or on the desk under the display), the Small Form Factor (even smaller), and the All-in-One (display and computer in one unit with separate keyboard). Of these, our experience is that the mini-towers have the longest lifespan and are the most cost-effective.
This may be due to the larger size, better airflow, or even the use of more common & available components, but to be sure we have seen over the past 10 or 15 years that the Mini-towers get a 10 to 20% longer lifespan then the other machines. That being said you may still want a smaller machine or need one due to limited desk space, but we usually say if you have the room and don't mind the larger box then go for the Mini-tower.
A laptop is usually about 30-35% more expensive than an equally powerful desktop or mini-tower computer, but if mobility is needed, then the laptop is the way to go.
One major difference between a desktop and a laptop is that they vary widely in physical characteristics. Whereas a desktop computer's monitor and keyboard are not part of the main processing unit and can be changed at any time, you are tied to your decision for these components when you buy a laptop. The size and weight of laptops vary depending on whether they are big, heavy and just portable or small light and highly mobile. In some of the larger laptops you can also find models that include a separate number pad which could be an attactive feature to someone like an accountant.
Based on these varying features we like to recommend that you get to see in person, either the actual model or a close model to the one you are interested in purchasing.