Small businesses tend to operate on a tight budget, so when the decision is made to rent or purchase new hardware, it isn't made lightly. With choices between Macintosh, Windows, or Linux for software, and the choice between Apple or IBM or Dell or one of a dozen other manufacturers for hardware, there are a lot of factors that can make this sort of thing a difficult decision. Budgeting for new or even used hardware is a question of balancing the dollars against the pros and cons of each upgrade.
In the 80's, Macs were the undeniable choice for any professional graphic designer or pre-press studio. Today, though, after decades of advances on both the Windows and Macintosh side of the fence, the operating systems are much closer in terms of capabilities, and will happily co-exist on the same network. Linux, while having the undeniably huge bonus of being free, has a glaring flaw in the fact that because millions of dollars weren't invested in making it as good as it can be, it's unreliable in many situations as the software of choice. Apple makes all the hardware and software for their Macs, which some would say is a good thing as it leads to better compatability, while Windows supporters will tell you that the benefit of the ability to run on any variety of PCs leads to more choice in your system specifications and better value for your money.
There are arguments between portable and desktop computers as well. The arguments for a portable laptop are obvious. Laptops can be taken to clients, are easily transportable between home and work, and take up a lot less space -- meaning you don't have to set aside an area for them. If portability isn't a concern though, there's really no reason at all to consider buying a laptop. The disadvantages are many, the foremost being cost. Desktops are just a better value at every end of the spectrum. Desktop machines can have much faster processors that would generate too much heat for a laptop, you can stuff more RAM in them, they offer faster and larger HDDs and the option to have more than one, and more powerful graphic cards. Let's not forget the benefit of having a 23" monitor when you're working with graphics.
Each side of the fence has distinct advantages and disadvantages, but in the end it would seem that if cost is your primary concern, a Windows-based system is the way to go. If you have a little more leeway in your budget and you want a system guaranteed to perform with no hiccups, you might want to consider a Mac. Each person's individual situation is going to influence their decision one way or another, so weigh your priorities and requirements, do a little research, and figure out what is best for you.
If you aren't ready to commit yet still need a computer now to do your work, you could try a laptop rental or desktop computer rental and have a test drive. Computer rental websites will deliver your computer to your home or work, and the examples shown above both carry a full line of both Macintosh and Windows-based computers and laptops.