I find it hard to pick just one favorite…
The first mode, though it seems like it’d be the most vanilla, does some cool things with sync and gets pretty interesting on the Aux output.
FM mode seems smoother than the one in Rings, though I haven’t done an A/B test to make sure of that – it could just be it’s very well suited to the internal LPG. I am an FM junkie, and appreciate having lots of variations available 
Waveshaping mode is fantastic IMHO. I was a Plaits beta tester since later December, and I sold my Tides, which was my first Euro module 
Harmonic and formant modes are very cool.
The vocal mode is suprisingly useful; just leave the trigger unpatched and navigate the phonemes with CV, or use it “frozen” on particular phonemes.
I get more use out of the green side than the red side, but then I don’t use a lot of drums in my music. Red for me is cool for abusing the noise and percussion models for non-percussion uses, feeding Rings, and accompanying Rings.