Legibility is the constraint that eliminates most candidates. Body text is read at small sizes on phones in poor conditions, which means condensed faces, decorative faces, and anything with unusual letterforms fail regardless of how good they look in a heading. Choose the body font first, on the basis of whether a paragraph is comfortable to read, then choose a heading font that sits well with it.
Use fonts that are widely available or served reliably, because a font that fails to load is replaced by whatever the device chooses, and that substitution changes your layout as well as your appearance. System fonts load instantly and render predictably on every device, which is a genuine advantage over a hosted font that adds a request to every page load.
Check the licence before using anything anywhere it matters. Fonts are licensed rather than owned, and the licence for desktop use frequently does not cover embedding in a website, and neither covers use in a logo or in an application. Free for personal use is a category that catches people out, and a font used commercially under a personal licence is an exposure that surfaces at an inconvenient moment.
Pair them by contrast rather than by similarity. Two fonts that are nearly alike look like a mistake, while a clear difference between a heading and body text reads as deliberate. The reliable approach is one distinctive face for headings and one plain workhorse for everything else, which is why so much good design looks like exactly that.
Consider the weights you will actually need before committing, since some families ship with two and others with a dozen. A family offering a regular, a bold, and an italic covers nearly every requirement, and a family missing a bold forces awkward substitutions that undermine the consistency you chose the font for.
Record the choices somewhere alongside your colour values, including where to obtain the fonts. The most common branding failure in a small business is not a poor choice but a document produced later by somebody who did not have the font and substituted something close, and that drift accumulates silently across letterheads, proposals, and social graphics.
Set them into your templates rather than selecting them each time. A document template, a proposal template, and a graphic template with the fonts already applied means every subsequent piece starts correct, which is what makes consistency achievable rather than effortful.
Then check them at the sizes you will actually use, on a phone, in daylight. A font that looks refined on a large screen can be unreadable at fourteen pixels on a device held at arm's length, and that is the condition most of your audience is reading in.
Limit the sizes as well as the faces, because uncontrolled size variation undermines consistency as effectively as mixing fonts does. Three or four defined sizes covering headings, subheadings, body, and small text is sufficient for everything a small business produces, and defining them once means documents look related without anybody making decisions.
Check how the fonts render in the places you cannot control, particularly email. Most mail clients ignore custom fonts entirely and substitute a default, which means an email designed around a distinctive face arrives looking like something else. Choosing a fallback deliberately is better than accepting whatever the client picks.