I'd fish the downstream side so that when the fish hit it would have to swim upstream trying to get back into the jam making it a little harder for it to tangle your line. On the other hand, it is harder to present your lure from downstream, but that's just one of the the things that makes fishing challenging.

That all depends on the type of fish, and how swift the water is. In a swift water flow and fishing for bass, the bass have a habbit of gilling for food. They get infront of an obstruction in the strong current and just open their mouth and let food pass into their mouth. In this condition, it is usually better to be above the obstruction. Fishing the jams on the wing dams of the Apalachicola River has been one of my favorite ways to catch bass. But if the water is not flowing hard, always go below the obstruction.

below. that's where the fish will be staging anyway.

Most of the times I fished in front of the jam it cost me alot of fishing gear that's why I tend to fish after the jam.