https://screenrant.com/best-sitcom-rivalries-funniest/

Rivalries such as those between Pawnee and Eagleton, Homer and Flanders, and Frasier and Niles are fan-favorite parts of their respective sitcoms.

The characters of Cheers and Scrubs were at each other's throat most of the time, I would've inserted them.
Frasier wasn't built on the rivalry between the brothers, if not on the most 'cartoonish' episodes. in fact they were very supportive of each other.

My fav 3 are:
Niles and CC on The Nanny
Al Bundy and Marcy on Married... with Children
Carter and Stuart on Spin City

I'd go with Endora and Darrin,

I'd go with Endora and Darrin,

Nice one!

Benson DuBois and Clayton Endicott III on Benson
Ted Lawson and Brandon Brindle on Small Wonder
Dick Solomon and Vincent Strudwick on 3rd Rock From the Sun
Morty Seinfeld and Jack Klompus on Seinfeld