Most years Harvard is much better than Stanford in fencing. But Princeton is usually better than both.
Besides fencing, Harvard is usually much better in rowing and squash. Our daughter is a varsity athlete at Harvard in a sport where Harvard is ranked much higher than Stanford, and academics come before athletics. This is true in theory and usually in practice too. She has several friends on other teams, and this is also true for them.
The Ivies have to adhere to the Academic Index requirements, can’t offer athletic scholarships, and if you compare the Common Data Sets of HYPS, you’ll reasonably conclude that there are probably at least 50 kids per year at Stanford who would not be admitted to any of HYP based on academic criteria alone. It seems likely that a great many of those are athletes. That’s the tradeoff Stanford seems willing to make to have the best overall athletic program in the country for the last quarter century. Their academics are broadly on par with Harvard’s, but it’s just a sportier place, and the weather (and the outdoor culture it fosters) bolsters that.
At a micro level, you’re going to care about the relative competitiveness of your sport, the amount of playing time you’ll get, your coach, etc. Stanford is not better in all sports, as has been pointed out upthread. Harvard and Stanford are very different environments, too, and not just because of the weather. For starters (again based on the Common Data Sets), Stanford has over 40% Californians and over 60% in STEM/STEM-related majors. Harvard’s much more East Coast-tilted and has more humanities and social science majors. Cambridge/Boston is very different from Palo Alto/the Bay Area. More Harvard grads go into finance/consulting, more Stanford grads work in Silicon Valley. Many factors may influence your decision.
Can I ask what your GPA & SAT scores are? I’m just trying to get a general feel for what the Ivy leagues will accept as far as grades and test scores. Thank you in advance!!
^^ It depends on the sport. I imagine helmet sports (football, hockey, baseball, wrestling, lacrosse) at both Harvard and Stanford have a lower test score and GPA threshold than a sport like track, fencing, crew or golf. For example, this from Harvard’s FAQ golf recruitment page: http://www.gocrimson.com/sports/mgolf/faq
So for golf, Harvard is looking for a 2100+ on the old SAT (1470+ on the new SAT) and a GPA of 3.80+, while taking a rigorous course load.
Thanks, I know there are many, many variables. In my sons case he is a baseball player who is currently talking to Johns Hopkins, Tufts, and some of the similar Calif schools. However, he also got an email from Yale & Harvard and we’re trying to gauge if that is realistic for him. He has a 3.9/4.1 GPA and scored 1300 on the new SAT. He also scored a 28 on a practice ACT test. Academically, he seems to be borderline Ivy at best…but it seems that if the coach really liked him that he might have an outside chance??
It really all depends on sports AND how much the school wants that particular athlete. Good example: Zak Farkes. In high school he was three sports superstar in baseball, football and basketball. He was captain in all three. He later played for the Boston Red Sox (I think he dropped out of Harvard to turn professional?). His high school GPA? 2.75. His (old) SAT scores were 630 Math, 630 Verbal. Harvard got him EA. Farkes didn’t have any other hooks. Of course, for most other athletes, they’d need better scores than these, I’m sure.
He completed his degree in time. as Ryan Donato H’19, who just signed with the Bruins, also plans to do.
I will, however, point out that Zak came to Harvard in 2002, which from an admissions perspective, is a lifetime ago.
FWIW: My son played baseball on the Stuyvesant High School Baseball Team (he was catcher) with Nolan Becker (as pitcher). Nolan was throwing a 91 mph fastball in HS (my son had to have extra padding in his glove, Nolan’s pitches landed that hard). Senior year in HS, Nolan pitched the only perfect game in NYC PSAL that year, was recruited by every ivy league school and ended up going to Yale. His junior year at Yale, Nolan was recruited by the Cincinite Reds – this was in 2012, so he could not play baseball at Yale his senior year: http://www.ivyleaguesports.com/news/2012/6/11/6_11_2012_170.aspx?path=baseball I don’t know Nolan’s SAT scores, but he did have an A average at Stuy, which is quite remarkable.
Yes, Zak’s case was a lifetime ago, but some things just don’t change…?
You know, if it were football or basketball, I might concede the point (probably not, though). But a 2.75/630/630 for baseball in 2018? Not gonna happen. We can, of course, agree to disagree. 
Not gonna happen these days. For sure.