For whole disk encryption (WDE) or any sort of password protected service where you cannot execute software (primary authentication), I encourage the use of pass phrases. Dice ware is nice. Something such as this:

"lua ham purple day girl"

The challenge with primary authentication passwords is that users typically cannot use a password manager or generator to recall the password and thus must be able to recall something that they can easily type and end-up selecting weak passwords. There are some exceptions to this (yubikey, etc) but most normal users don't or cannot use them for various reasons, so go with a nice pass phrase like the one above.