I generally ski in the trough. The softer it is, the more time I'll be in the trough. Slushy bumps are the most predictable surface. If it's warm outside, then I know what the conditions will be like, and I love it, so I'll head up to the mountain. Other people seem to feel the same, because once the weather gets warm, you'll see lots of bumpers out there, especially in regions that are powder deprived. I've often skied in 70 degree weather in some of the slushiest conditions we ever see, where many people refuse to come up to the mountain, which is another nice thing, the mountain is empty except for the bumpers. I don't enjoy groomed run conditions as much when it's that warm, but as long as there are bumps, I'm having a fabulous time. The slush provides so much drag that the bumps are effortless. In any type of soft conditions, I'll be in the trough. With very narrow bump skis, there's no skidding in that extreme slush which is why many people have trouble with it. You have to use properly timed absorption and extension going from edge to edge. Speed control comes from controlling forward pressure and absorption and extension. Very slushy bumps are considered "hero bumps", because they are so forgiving. However, because lots of people are skiing in the troughs in these conditions, and because it's so soft, the troughs can get cut extremely deep when there's lots of traffic. You end up with very deep holes that start demanding deep absorption, and some people start riding further up the front side of the bump or skim from top to top if they really want speed, though I tend to stay in those deep holes and go slower, because I like it.
So, here's when I'll avoid the trough. When it's extremely icy and you get a few inches of snowfall, that extra snow is almost instantaneously pushed off the backside and out of the trough. All the powder accumulates on top of the bump. So, in those conditions, I'll avoid the troughs and turn on the topside in those clumps of powder.