Use the "passwords" feature to check if one of yours is compromised. If it shows up, never ever reuse those credentials. They'll be baked into thousands of botnets etc. and be forevermore part of automated break-in attempts until one randomly succeeds.
As always, the most secure password is the least convenient and accessible. It's a trade off, but you want fewer dictionary words and patterns overall. Preferably with a physical component for the master password.
Longer is better...giggitty.