I think it depends on the film in question -- its genre, its subject matter, its tone. The benefits of black-and-white and/or color photography work for some things better than others.

These examples are based on my own personal taste and humble opinion; I'm certainly not trying to lay down any laws...

To start with the reason we're all here, horror films, especially the traditional gothic sort that deal with the supernatural, seem for me to be better in black-and-white. The shadows, the fogs and mists, the interior architecture of the castles, towers, mills, etc. of seem to take on a tactile silkiness that I find aesthetically pleasing. Likewise the costumes and makeup; given extra depth by the infinite shades of gray.

The same could be said for mystery/detective films; whether classical or film noir. Sherlock Holmes and Philip Marlowe seem naturally more at home in a shadowy black-and-white universe.

Westerns, on the other hand, greatly benefit from either palette. When showcasing the grandeur of the American West, either an Ansel Adams-style black-and-white or a glorious three-strip Technicolor can create sublime beauty. See John Ford's My Darling Clementine and The Searchers for perfect examples of the former and the latter.

Adventure films, for me at least, work better in color; especially Technicolor. It's hard to imagine a black-and-white James Bond film, or North by Northwest, or Jaws, or The Adventures of Robin Hood, or The Hunt for Red October. Color just seems to amplify the bigger-than-life aspects of these stories.

Comedies, romances, musicals, and straight drama can go either way. At this point in the history of cinema, when color is almost 100% standard, to do these types of films in black-and-white is something of a fashion statement on the part of the filmmaker. The technique calls attention to itself; in McLuhanesque terms, it becomes part of the film's message.

Probably an unnecessarily complicated answer to a simple question. :-)

Vlad
The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents.
-- H. P. Lovecraft