Well it depends on the position and the unit composition they have to be honest. Mortar smoke barrage is great at covering an advance while you get into a good cover position. 222's force engagements at max range if you dont think there is a zis gun around.
You'll have to be a little more specific. There are many ways to "assault" a position, and the best one is highly situational
I've always really liked smoke. I need to go back to using it more often. I got spooked though, for a long time it seemed like a coin flip as to whether a barrage would actually launch or not.
I'll have to start playing some more and get some replays, but It seems the majority of engagements I run into are entrenched conscripts. Building cover is so quick, and naturally very effective, it makes them difficult to dislodge.