My fave is currently the Bass Big Muff, only for the simple reason that it sounds awesome with an overdrive going into it with the BBM set to blend mode. I like to have layers to my gain, kick on the SFT for a bit of a boost, then add the Muff on top when things get heavy. This way there's less tap dancing going on, the blend retains some clarity and dynamics but without sounding like 2 separate sounds since I'm already feeding in a dirty signal. The gain boost also helps to give the BBM kick it needs to make it sound super heavy and saturated. I also added a feedback loop mod too, which sounds great on the Muff circuit.