SPOILER ALERT: QC3 Pleather + Mikros foam sounds the best.
Stock Mikros: These ime definitely have the most sibilance. The seal is nice, just too much sibilance going back to them now after the other pads.
Beats Solo: Good pads, but not without issues. They recess the mids, taking you out of the music. I don't like it. Also, they're the most uncomfortable of the bunch since they trap in air too well.
QC3: It does away with the sibilance, slightly reduces treble, and helps the soundstage. Vocals sound slightly clearer, and bass is improved slightly in extension and tightness. They feel the same on my ears comfort wise as stock.
I'm planning on modding the QC3 pads' foam to make them similar to stock. We'll see!!