The biggest problem with Bitcoin is that it is so hard to predict when you must buy it or sell it.
I think that is a really hard choice to make we you going to sell it, there is a chance that after you sell it that it can be more worth later in the future.
It is not Bitcoin specific, any stock is not easy to predict when you must buy it or sell it. The information + trading experience is what separates loosers from winners in these trading games. If your not experience trader, best is just to hold Bitcoin (or stocks) and sell only when you really need money.