For me it's Zender. I love the others, but Zender has something that really clicks. I think he is more economical in his fills and lines, yet his basslines stand out. They are really the linchpin of the songs, in a way like Flea does. Emergency On Planet Earth and Travelling Without Moving are the definitive Jamiroquai albums for me. The following albums are a bit too disco and overproduced for my taste. The other players groove really hard, but Zender had something extra. Less is more I guess.