One space or two?

I was taught in typing class way back when to hit the spacebar twice after a period at the end of a sentence. For decades I did that. I was a zealot for double spaces.

Then I was told that computerized typography adjusts for the end of a sentence and I no longer needed to. Now I'm a zealot for single spaces. Nothing makes me crazier than coming across my own earlier work with double spaces. I get all OCD and want to change every one.

So what should you do?

Wikipedia notes the controversy, and concludes:

Many experts now say that additional space is not required or desirable between sentences. Typesetting programs such as TeX can modify kerning values to adjust spaces following terminal punctuation, so there is less need to increase spacing manually between sentences (provided that there is some cue to distinguish the end of a sentence from the end of an abbreviated word). From around 1950, single sentence spacing became standard in books, magazines and newspapers.

So Wikipedia sides with me. Let's check in with the authoritative Chicago Manual of Style. Answering a question online, one of its editors asserts:

The view at CMOS is that there is no reason for two spaces after a period in published work. Some people, however—my colleagues included—prefer it, relegating this preference to their personal correspondence and notes. I’ve noticed in old American books printed in the few decades before and after the turn of the last century (ca. 1870–1930 at least) that there seemed to be a trend in publishing to use extra space (sometimes quite a bit of it) after periods. And many people were taught to use that extra space in typing class (I was). 

But introducing two spaces after the period causes problems: (1) it is inefficient, requiring an extra keystroke for every sentence; (2) even if a program is set to automatically put an extra space after a period, such automation is never foolproof; (3) there is no proof that an extra space actually improves readability—as your comment suggests, it’s probably just a matter of familiarity (Who knows? perhaps it’s actually more efficient to read with less regard for sentences as individual units of thought—many centuries ago, for example in ancient Greece, there were no spaces even between words, and no punctuation); (4) two spaces are harder to control for than one in electronic documents (I find that the earmark of a document that imposes a two-space rule is a smattering of instances of both three spaces and one space after a period, and two spaces in the middle of sentences); and (5) two spaces can cause problems with line breaks in certain programs.

So there you are: the ancient Greeks are on my side. And they were some pretty smart dudes. Even their little children with cute garlands on their heads playing video games in the Parthenon spoke Greek fluently.