What credit reporting agency is used the most?

[Dru]

Experian? Equifax? Transunion?

Which credit reporting agency is used the most to determine APR etc trade lines?
Please backup your answer as to why you are choosing that agency. I'm basically trying to find out which one is the best one to sign up for the score watch.

 

[DAS]

All three, this is the top three, and they all are used.

 

[Robin D]

in my experience it is equifax