Technical vs. fundamental approach
Many discussions are going on whether technical analysis (and thus trading systems) or fundamental analysis is better to be successful on the markets. To my mind, instead of asking "whether...or" one should affirm "...as well as..."!
Fundamentals are very important and in the long run, fundamentals are the one and only driving market force. However, the shorter the time frame other factors become very important like psychology and market sentiments which have all been described and analyzed in the theory of Behavioral finance. Furthermore, the complexity of our world in general and of the markets in particular (electronic markets, complex instruments like CDOs, possibility of short-selling and over-leveraging, etc.) can cause movements which often can´t be explained by fundamentals and which are often interpreted as market-misbehaviors.
These situations (which usually persist only during a short period of time) can be exploited by computer software, i.e. trading systems. As I showed in my Publications many profitable systems exist for those situations. It is also possible to use systems which use a longterm approach (mainly trendfollowers) and a lot of successful money managers are using them. But since fundamentals are the driving force behind longterm movements a stronger weight should be put on fundamentals for these kinds of investments.
So, in general we can say:
The shorter the time frame of our trades, the more important become trading systems.
The longer the time frame of our trades, the more important become fundamentals.
So, I do believe that the optimum trading strategy is a good balance of both fundamental and technical analysis together with a reasonable risk- and money management.