Wading upstream makes more noise and takes a lot more effort. I usually go downstream as slowly and quietly as possible and try to stay out of the current as much as possible. Stay on the opposite side of where you want to cast to and you can still make most of your casts upstream.
There can also be some benefit to stirring up the creek a bit. You are also stirring up food and getting the predators ready for a meal.
I hate to go against the current, and thread, in this situation, but Streamstalker is dead on about stirring up a creek. One of the best kept secrets of some of the older folks who have been doin this for years. Up or down, you still have to stalk each hole quietly and plan an approach.
I primarily wade upstream and cast upstream when stream fishing. I've always done this because of reading an article that says fish face upstream. This way my lure comes downstream with the current. If I do wade downstream, I will still cast upstream or across the stream and let the current swing my lure where I want it to go. There is advantages/disadvantages to each.
wade upstream. not only does it make it easier for you to catch fish. but it is also easier getting back to you car. when you are tired from going up against the current it is nice to be able to walk with the current