Which should I use? In other words, "to dot or not to dot"?
You know what? Both ways are acceptable. In American English (in other words, the wrong way*) they keep the dot — in other words, they write "Mr.", "Ms." and "Mrs." — and in British English we mostly just write "Mr", "Ms" and "Mrs".
As you no doubt know, "Mr" is an abbreviation of the word "Mister". The word is an alteration of the original "Master". Nowadays you would use "Master" to refer to a young boy: "Young Master Daniel looks so handsome with his curly hair". (I used to get that a lot, believe it or not.)
The plural of "Mr" is "Messrs", pronounced "messers" (as in, people who mess things up), which comes from the French "messieurs" (meaning "gentlemen").
"Miss", "Mrs" and "Ms" are all abbreviations of the word "Mistress". With the modern meaning of the word "Mistress" giving connotations of illicit, extramarital affairs, you don’t tend to hear it that much these days. Except if you’re an over-officious protocol droid, of course, in which case you’d probably use it a lot.
The plural of "Miss" is "Misses", although I can’t ever remember hearing it; the plural of "Mrs" is "Mmes", an abbreviated form of "Mesdames", from the French, er, "mesdames" (meaning "ladies"); and the plural of "Ms" is "Mses", although "Mesdames" can also be used.
The default way to refer to a man would be to use "Mr & Surname", unless you know he prefers to use a different honorific, such as "Dr". More and more these days, the default way to refer to a woman would be to use "Ms & Surname" (unless, as above, you know she prefers to use a different honorific, such as "Dr"), and that sounds right and proper to me. It’s bizarre that men’s marital status doesn’t ever come into the equation, while up until relatively recently you’ve been obliged to use "Miss" for unmarried women and "Mrs" for married women. Who cares whether or not they’re married?
Postscript revision! My good friend Claire (who's a wonderful copywriter and is about to launch her own website) reminded me of the "Pride and Prejudice"-era form of using "Miss + Surname" for the eldest unmarried daughter of a family; every other unmarried daughter would be know as "Miss + First Name + Surname". So you'd have, for example, "Miss Jackson" and her younger sisters "Miss Claire Jackson" and "Miss Marguerite Jackson".