I've been using Dunlop Tortex 0.5 mm (red) since they first hit the market. A thin pick gives me much better control over the sound, especially when I'm strumming chords. A guitar should be stroked for rhythm parts. Heavy picks tend to scrape. A thin pick gives me more subtle attack and release, the same way that a slightly soft-strung tennis racquet gives more control over the ball.

I hold my pick so that the edge of the pick touches the string first, sliding toward the tip. There is no clackclackclackclackclack from the pick lurching free of one string and crashing into the next one. After I've used a pick for a while, the edges are actually quite sharp from sliding past the strings.