Did you see Devil Wears Prada? If you don’t want to memorize a book of headshots for your host, plan on printing nice nametags everyone can read, without looking like they’re reading them.
Font sizes? If using standard 3x4 tags, I prefer Arial font size 40 for the first name, on the second line the last name in size 26 and two spaces below this, the company name in size 26.
Name tags should include the person’s first and last name and company name. I tend to omit titles other than those who are hosting the event because titles change every other week (you may have a "not so understanding" guest because you didn’t get the memo of his promotion yesterday) and titles often are too long for the space allotted.
Do you really need nametags? I asked this years ago to an executive I truly admire, and was told, “I expect nametags at my funeral.” We had nametags at every event.