Which of the following would be the best password attack for him to choose if Jack is tasked with testing the password strength for the users of an organization and he has limited time and storage space?

A dictionary attack is a type of brute force attack that uses a list of commonly used passwords, also known as a dictionary. This means that it requires less time and storage space than a brute force attack, which tries every possible combination of characters.
A rainbow attack is a type of precomputed attack that uses a table of pre-calculated hash values. This means that it is not as effective against passwords that are regularly changed, as the hash values in the table may not be up-to-date.
A keylogger attack is a type of attack that records the keystrokes made by a user. This can then be used to steal passwords and other sensitive information. However, this attack requires Jack to have physical access to the user's computer, which is not the case in this scenario.