The safest password is a long password. Simply put. Myself I have a list of 20 passwords that I always use and continually recycle the list. One would think that's a bad idea but it's pretty secure and efficient.
But to the question: I choose favourite quotes or lines from books.
Take these examples:
Both passwords are strong but the first is considered insanely strong despite the lack of special characters, numbers and only one Capital. Why? Length. What's better that it is a fairly easy password for a human to remember. but it'd take quite a bit to brute force it.
You see a password makes little sense if it's so complex you have to always write it down or risk forgetting it. Using proper sentences on the other hand creates personal, easy to remember and hard to brute force passwords. If the site allows for characters like punctuation marks then you can get some hellish complexity.