I’d be asking myself what it is about the Sub Phatty that you find lacking and go from there. (For me it’d be the small number of presets, short keyboard and the fact that lots of hidden options are only accessible via convoluted multi-button presses. Subsequent has almost all of its info accessible from the panel, and the menus, when needed, aren’t too deep.)
Can’t fault the sound of the Sub Phatty - its beastly.