For acoustic guitar, I find a thin pick too sloppy--that is it springs back and forth more that you can control..

I use picks like Jim Dunlop .88mm and 1mm. I like to be able to control which strings I hit when I strum--I tend to incorporate some runs and partial chords within the particular chord I am holding. And a heavier pick is needed for this.

And flatpicking melodies don't work with skinnypicks.