The size of the print isn't as important as the length of the repeat. You want a large scale print with lots of contrast (unless you are making a small block...then you want a smaller print with lots of contrast). Lots of contrast is the key.
To find the repeat, pick a design in the quilt then look for the next identical design going lengthwise down the fabric. Measure the distance between the two designs and that is your repeat. Each pattern will call for a certain number of repeats. There is no set measurement for repeats. They vary from fabric to fabric.
Hope that helps. I know it's confusing.