It depends on where and how the figures are shown.
On a website, with suitably zoomable pictures, I prefer seeing both; some nicely painted pictures and one or two pics of the aforementioned black wash.
The reason is that the type of miniatures that draw me in (fantasy and scifi) is usually covered in fancyful detail which can be unclear when not well painted. This contrasts with historical miniatures, which tend to be less cluttered and every aspect of the uniform and kit is well known, and plain, simply washed miniatures are just as suited.
When at a show, I prefer painted though, period. Well painted miniatures on display are what sells the minis as far as I'm concerned.
In magazines, I don't care either way, as long as the pictures are sharp enough.
When I say painted, I don't mean painted to a ridiculous Golden Daemon standard; it's much better to have a well defined, crisp paintjob that highlights the miniature's features than one overshadowing them with fancy colourfades, over the top highlighting and elaborate freehanding.
Oh, and bad paintjobs which obscure or omit details, go over 'the lines' or otherwise mess with seeing the miniature underneath well, should most certainly be avoided. We're better off with a simply black wash in those cases.