What’s Your NFL teams biggest rivalry?

Just wondering, as far as your personal favorite team goes: Who is your favorite NFL teams “biggest rival” or biggest foe? For me, I cheer for Denver Broncos, so I would have to say the KC Chiefs or Las Vegas Raiders would be our biggest rivalry games we have during the season? What about you? Who do you cheer for in NFL and whos your biggest rival you cheer AGAINST in the NFL?