Crit value scales with your gear and can roughly be calculated. For pre-raid gear it's 30-32 RAP per crit and goes up to 35-38 in later stages of PvE progression.
If judging Agility vs. pure AP take the rule of thumb factor 2.5 for Agility as it also gives crit.
Example: 2% crit or 1% crit and 50 AP.
~64 AP against ~82 AP. Dal'rends is the clear winner.