That depends. I normally like to stick with the basics -- Arial or Times New Roman -- because they tend to come out pretty much the way you had inteneded. If you choose some other font and the printer doesn't happen to have them available, you may end up with something similar but not quite what you selected.
You can overcome this in some file types. Some file formats like PDF allow you to embed (include) the font in the file which can help in some situations but you have to tell it to do so.
If you provide a luxury service, you might consider more of a script font.
The font size should be between 7 and 9 point, with the name of the company being no more than 11 point.
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