Well a mix of both really. I start with a hard edged brush (usually the stander PS chalk brush) and use that for the majority of my painting. But i switched to the standard soft round brush to add over all lighting/ colour changes and the subtle areas of fog creeping in. I also tried out a few custom grungy brushes for the foliage. And yes i pretty much always use 100% opacity, and i usually use pen pressure to control size and opacity of my strokes.