"Now, Watson, the fair sex is your department."
-- Sherlock Holmes, "The Adventure of the Second Stain"
I think we can take Holmes at his word here both in what he says and in what he implies about his own shortcomings in this particular field.
Watson was married at least twice, maybe three times. His reference in The Sign of Four to his "experience of women which extends over many nations and three separate continents" seems credible; Watson, after all, is no more a braggart than is Holmes.
Michael Hardwick, in his 1983 novel The Private Life of Dr. Watson, fleshes out the details of those encounters -- sometimes with a little too much flesh for my tastes. One of his early chapters is titled with the quote above.
Of the duo it is Watson, not Holmes, who would have been the natural choice to romance Charles Augustus Milverton's housemaid to get information. But, of course, Watson would never have done such a caddish thing -- and he is aghast that Holmes did. "Surely you have gone too far?" he says. And then, "But the girl?"
That's our noble, ethical Watson -- equally ready with a gun and with a handkerchief. He is a man's man, and woman's man, too. However many wives he had, I'm sure that each one thought quite correctly that she had landed quite a catch.