The nice thing about jelly rolls is that you get a strip (or 2) of each fabric in a fabric line. Of course you pay more for the precut. Using yardage to cut strips works well too. It takes your own time and you can cut the strips to the size you like. I like to mix jelly rolls with strips from my stash (or new-bought yardage).
It helps to have a pattern in mind when making the decision. Have you checked out the tutorials on missouri star quilt company?