Definitely La Bella for flats. I use Circle K, which I am very happy with, but I know a dude that uses the La Bella flats and they sound incredible. Monster player too.
Fyi, the Circle K set that I use is: BVI-102 - 102 76 57 43 33 23p.
3Leaf Audio Club #93; Source Audio Sourcerers Society #134; Squier VM Bass VI #3