What's the best diaper bag in market now? Preferably a backpack..

My friend has the Marc by Marc Jacobs "Nylon Eliz-a-Baby" diaper bag and she loves it. Actually I love it too haha! It's pretty decent in terms of storage and material. But I reckon, this piece is more fashionable than it is functional. There are definitely other brands that are cheaper and more durable out there.