--- This, probably, is the one to buy. But decide for yourself...
--- The New Oxford American Dictionary (NOAD) may be regarded as the American translation of the New Oxford English Dictionary (NODE), published in England in 1998. A great many definitions are word-for-word identical between the two works. However, NOAD introduces significant improvements.
--- For example, NODE omits pronunciations for "ordinary, everyday" words, and as a result you get no hint as to whether "corgi" rhymes with "orgy" or "Porgie". NOAD provides pronunciations for all words, using a more sensible respelling. Furthermore, entries contain raised dots to separate syllables. Unfortunately, the dots are more prominent than the hyphens, which are mere flyspecks in both dictionaries even though that is precisely the sort of information a user might need.
--- NODE has no illustrations, which are abundant in NOAD. The crude maps are close to useless, and many pictures are mere eye candy, but some are worthwhile, for example the illustration for "pasta", where you may encounter "orzi" for the first time.
--- A great many NODE entries have been deleted, especially those for Indian, Australian, African, and some British English entries such as "gain-up", precisely the items that might send an American user scurrying for the dictionary. Proper names of British import are frequent casualties. On the other hand, many American entries have been added, including the New England beverage "frappe", but not "tonic". Wherever NODE indicates that a word is "American", that designation is omitted, whereas NOAD supplies "British" for other entries. Of course, the fact that a particular word is "American" will often be of interest and perhaps importance to an American user.
--- Spellings have been Americanized, and some entries, such as those for "corgi" and "Welsh corgi", have in effect swapped places.
--- Political correctness is sometimes apparent. Someone decided there should be a new entry "altar girl", which (mutatis mutandis) is a clone of NODE's entry for "altar boy". Someone else decided that the definition of "altar boy" could be recast in terms of "altar server", but the latter term received no entry of its own. The result is a curious lack of parallelism that might lead readers to suspect that altar boys and girls have dissimilar functions. Something of the same sort befell the entries for "chairman" and "chairwoman".
--- NODE's etymologies for "cola" and "Coke-bottle" may be regarded as adequate, but since NOAD deleted the entries for the trademarks "Coca-Cola" and "Coke", the etymologies no longer suffice. NODE has an entry for the archaic exclamation "gad", which NOAD retains, while adding an entry for the interjection "Gad" with virtually the same meaning. NOAD's deletion of the ballet term "chaine" is hardly complimentary. In the entry for "gigabyte", NOAD places a digit and its exponent on separate lines, albeit hyphenated. The introductory matter retains "homonym" in a chiefly British sense.
--- The cover claims that NOAD offers a "descriptive picture of American English", which often seems to mean they have not put themselves in the user's place. You will have to go elsewhere if you seek clarification of "chinks" as used in "Romeo and Juliet" or "Shakespeare in Love". If you read that Buddha was sitting under a bo tree and desire further information on this botanical specimen, you are unlikely to be enlightened even though NOAD has the information. If your mother says you have "hazel eyes", you will think her color-blind if you rely on the NOAD definition. For a generation, most Christians have celebrated "Passion Sunday" a week later than NOAD indicates.
--- NOAD is probably the first one-volume American dictionary to include such avifauna from our 50th state as "ou, o'o, iiwi"; it's the first to include the Madagascar birds "asity" and "fody", but "jery" remains to be discovered.
--- For sheer browseability, NOAD is outstanding. It's a great book to have at your side if you are the phone-a-friend for a Millionaire contestant.
--- All the above quibbles can be multiplied a thousandfold for this or any work based on millions of decisions by dozens of people. As the owner of more than fifty English lexicons, I would recommend this one-volume dictionary over all competitors. Consider purchasing it with CD-ROM (not available when I bought mine). If the price or size of this dictionary is beyond your grasp, a reasonable alternative is "Webster's New World College Dictionary", which incidentally gets "chinks", "hazel", and "Passion Sunday" correctly, while concealing the information for "bo" in the same way as NOAD.