Businesses typically have slightly different demands of their PCs that home users. Not surprisingly most major hardware vendors market PCs designed specially for business.
Regarding laptop PCs, business-grade units are typically more durable, feature better warranties, and often have the ability to “dock” the laptop, which makes it a breeze to connect to monitor(s), keyboard, mouse, and a wired Ethernet connection. Compatible docks can usually be purchased at a discount on sites like Ebay, but be sure they come with the required (and genuine) up-sized AC adapter. We have a lot of experience with Dell Latitude and Precision lines and have yet to be disappointed.
Speaking of durability, if your laptops are exposed to particularly rough or hazardous environments, consider a rugged or semi-rugged laptop. Such units are outstanding for use by maintenance departments or out on a shop floor. Semi-rugged units usually start around $2,000 new, but can be obtained used for a steep discount (good-shape units can be had used for as little as $400).
Desktop PCs don’t necessarily come with additional features that we tend to rely on, but they do often have better components and more generous warranties. You can usually purchase a business-grade Dell OptiPlex for only a small premium over one of Dell’s home-oriented models. If you are motivated to do so, business grade desktops do frequently feature centralized management features that can, for example, alert you of hardware issues that may be leading to a failure.