In what sports are men men and women athletes most or least likely to marry? 

The least likely sport for marrying appears to be professional golf. The only couple I can think of off the top of my head was Gardner Dickinson and Judy Clark-Dickinson. The husband, who was 23 years older, had pretty much retired by the time they married. The PGA and LPGA tours are separate, except maybe for one week per year during golf's silly season, so men and women pros seldom get together. In contrast, male and female tennis players get together at several championships per year. Male pro golfers generally marry women who like being home with the kids and house while they are travelling on tour. '

Similarly, I can't think of any NBA-WNBA couples.

In contrast, my impression is that track and field athletes are most likely to marry each other. Blacks don't get married at a particularly high rate, but black women runners often hyphenate their last names after marrying a male track & field athlete. Traditionally, track was an upscale sport among African-Americans, the spring sport at black colleges instead of baseball. Men's and women's track meets are typically held together, and they tend to be hurry-up and wait affairs, kind of like a movie set, another famous locus for romance since there isn't much else to do.