A decade or so ago, because I had to learn it for a school recital and know the poem backwards, I used Jabberwocky: Tbatstdgag1tw! - according to security.org’s password-strength-checker [1] that will take a computer 200,000,000 years to crack, presumably on average. I use a longer one today, and I skip words too, and some words I use 2 letters from - a similar string of characters to my current password is estimated at a trillion years.
At one point, I was using the first 2 lines of “Sea Fever” by Masefield, but that got too long to type - ImgdttsattlsatsaaIaiatsatstshb … If you’re interested, that’s 2 septillion years. I don’t need to be that secure :)