Listening to the mk3 off the lg v20. Steaming Plastic Picnic on Tidal. Like Chinmie says, the tuning of the Mks (revision 2) is similar and it's about individual preferences. The mk1 has more subbass and slightly pulled back mids and an intimate soundstage (not congested or small in anyway ). The mk2 punches more cus of its elevated mids which makes it warmer and the highs extend higher - its a crisp and airy sound.
The mk3 is a surprise, it has excellent imaging and separation like the mk2 with a faster bass response as the midbass is more controlled. By controlled I don't mean that they don't have bass impact or lack bass, they just have the right warmth and sound balanced. The guitars are crunchy and nice, they seem to be able to play far out of my head with the synth effects panning effortlessly around my head. Like the mk2, I'm able to follow all the sounds. The trebel is very slightly pulled back than the mk2, but not in a way that it's dark.
To my ears all the willsounds have a very good timbre and tonality, they sound natural.
Also, the mk3 look sinister in all black. I believe with the Mk series, you can't go wrong with either the mk2 or mk3 if you're looking for an all rounder.
Coming to the pk32 its like a baby mk 2/3. The mids are full and upfront , intimate. But the bloody bass from the size of those shells is atrocious. It's nice bass, warm n defined. Very good balance. As much fun as it's bigger brothers. Would love to see a comparison with the shozs bk when Sean gets his.
If you like musicality and a natural but fun response, it's hard to go wrong with any of the willsound buds.