Fonts with serifs or without?

Serif typefaces are traditionally used in print for the main text. As was already said above, the notches help keep the line, and his eyes less tired.
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For the withdrawal of the text on the screen, you can use a sans serif font, but decided to increase the line spacing distance. The meaning of this action is the same — to help the eye to keep the line, to visually separate them.
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The titles often make the contrast design to the main text, i.e. if text is typed in a sans serif font, the title is type a serif font and Vice versa.
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The source code issue is always very horrible about any printing to the value of that speech, as a rule, is not; use both the font family in about equal measure.

IMHO (I'm not a designer)
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Just remember. When at school in the last century were taught to write with a pen, specially taught to draw at the end of the beautiful lines of dots.
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Print — font with serif. On display — sans. Serif typefaces remain legible for longer destructible media such as paper. Sans serif fonts easier to read because they are simpler form.
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Special design solutions can do the opposite — for example, if You want the site resembled a paper newspaper, or book.

The ticks are invented to view to hold on the line, when a lot of the same type of text such as a book or a newspaper. Sans serif used for headers.
But this is more Convention and tradition, now neither one nor the other in no way inferior to any problems.