Interesting article with some maths about passwords here
One of the concluding paras says
The obvious conclusion for users is that they must choose their passwords randomly. Some software does provide a random password. Be aware, however, that such password-generating software may, deliberately or not, use a poor pseudo-random generator, in which case what it provides may be imperfect.
Truly random passwords are harder to hack but not easy to create and even less easy to remember!