Rivalries are a college thing. Close call, but I chose Cal v UW. It is special. These two heavyweights row at such a high level and have been kicking each others butts for so long. The history. All those Olympic gold medals (and you had to get past the other to make it to the Olympics). All those national titles. Plus, every other year you get the adrenaline rush of racing on the cut. No better venue anywhere. Like rowing at the super bowl only louder. Exhilarating to hear all that noise.
Harvard-Yale is a close second. The overall rivalry between the universities is better than Cal-UW(Off the water, it is Stanford that is Cal's rival on the athletic field and in the academic halls). And their history is longer and comparably as stellar. But the rivalry on the water has been less consistent and historically they have been more interested in playing with themselves then racing the rowing world.
Oxford v Cambridge is a great rivalry, but it is a one and off spectacle. I like that the other races are part of a season against other crews and with UW and Cal they meet each other at the dual, the P10s and the IRA.
Internationally, I love USA v CAN men the best. But it is really not the rivalry, but how you do at the multi-boat championship that counts. There are no bragging rights if USA finishes 4th and CAN finishes 5th.
Nothing against high school rowing. The rivalries are great. But they are local both in time and space. They kids may be good, but they have not yet reached their prime. They will get faster. College rivalries are more transcendent.
Oxford Cambridge is older than time, and its watched more than any of those other things, and they are always both fast. Game over. No discussion. Let us stop the tomfoolery and pettiness and give credit where credit is due.
IRAs last year was sick
Cal, Washington ................................................ Cornell, Harvard, etc...