Times New Roman fits well in extended pieces, such as newspapers and books, because to its readability. Arial, on the other hand, is more commonly employed in ads because to its clarity and relatively large characters. Arguably, though, neither font is particularly professional. The first word that comes to mind when thinking about a "professional" typeface is "bold". Indeed, there are many bold typefaces available, so it's not necessary to use a single one of them. Instead, choose a style that's appropriate for the purpose at hand. For example, if you need a headline typeface, then a sans-serif font works better because it's easier to read long-winded articles. On the other hand, if you have a brief message to send out, a serif font looks better because it gives your lettering more character. In terms of cost, Times New Roman may be worth considering because it's one of the most popular fonts in the world and therefore has widespread availability. It also tends to be cheaper than other more unique fonts. That being said, Arial is useful because even if it isn't purchased separately, it's often part of a basic license package that many software companies offer.