When I started the thread asking the same question ... one poster mentioned she went with different sizes and shapes but all the came multiple.
Why? because some fabrics the print runs long and narrow, some are wide. Some are big prints, some small.
Eg. ... finished sizes .... 3x3", 3x6", 6x6", etc.
That way, you've got some variation in your blocks, yet they all come together easy enough when piecing.
They could be randomly placed ... or strategically placed according to sizes.