Prime Factorization: My single favorite topic on the GMAT. It’s not even a contest.
My passionate (some would say evangelical!) advocacy of prime factorization results not only from my finding prime numbers so inherently fascinating in and of themselves, but also from the plain and simple truth that prime factorization proves surprisingly useful on questions on which prime numbers aren’t even mentioned.
For example, any time you’re given a question asking about multiples and factors, you can bet that prime factorization will help you get to the answer quicker.
Case in point — this Data Sufficiency question from the Official GMAT Guide: