The MP slouches, but it shouldn't crease. The lrge also has protective feet on bottom,and can keep unzipped while juggling baby! -- I was always grateful for easy access & durable when my babies were young!!
Of the two bags looking at, I think MP is a great all around bag. Mine is 2004 and still going strong --- no creases, slight wear on piping and a few spill accidents! - But Black can be retouched if that happens.