Atlas - West Blue
It is not clear how weak or strong West Blue is actually. But since East Blue is the weakest of the four Blue´s it´s clear that West Blue is stronger then this one. The little amount of West Blue places that have been shown or mentioned so far are listed below.
Places already visited by a Straw Hat Pirate:
Unlike East Blue West Blue is not place where the Straw Hat Pirates were traveling so far. However right now the manga is telling Nico Robin's past which took place in West Blue. Which gives this sea a little bit of a familiar flair. The only known place that falls under that category so far is: