I trade both discretionary and mechanical and both have their advantages and disadvantages.
In mechanical, it's very difficult to find a system that will get you the robust system before failing. Huge learning curve to get there, but once you're there things get easier (same as discretionary). When you finally found one good one (backtested and walk forward it), the real test is how much you'll leave it alone or interfere with it. Psychology has a major impact in it. I thought when I decided to trade mechanical, emotions would be the least of my worries. Wrong, your baggage goes with you as well. It relieves your entry decisions, but it's the taking profits or let it run is where you'll be your own demon.
Trading someone's system is a difficult task too. Have to do due diligence if you plan to lease someone's system, drawdowns, trade frequency and slippage and commissions being added to the performance report or not. There tricky vendors out there touting their systems, but do alot of homework before wasting good money. If you plan to lease them, stay away from daytrading or frequent trades systems and stick with swing or longer. After 2 years of research and system building, I found that the higher the time frame or less frequently traded the systems, the more robust they are. You can see for yourselves some vendors are automated systems:
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Although eSignal does do automation, I use and recommend tradestation for building trading systems as well as automate them to trade by themselves, there are also traps to them. After 2 years I found 2 systems that seem to stand the test of time (5 yrs of backtesting historical data and 6 month in walk forward or real time testing), one swing and one daytrade and they trade every other day and not more. If you plan to build trading systems, start with higher frames (60min or higher), then chances of finding good systems.
You can have a look at mine. I'm not selling it but it's for my own record-keeping and personal journal.
Trendhugger | One Trend.
Good luck.