Studying and reviewing world history...?

Would recommend both if you wish to really learn about world history and retain more of it this time around. What you miss or under-learn in one book, you'll have a second chance to capture and nail when you study the second book!! Also, one will re-enforce the other because the same facts will be presented differently - this is called "synergy", where two or more things work together to produce a stronger effect than just one could alone.