From time to time I get asked during interviews if I trade other asset classes during the trading day. My answer is always yes and no. I do longer term swing trades in the FX market but no, I do not trade both FX and equities intraday very frequently. When I do I tend to lose my focus and do not trade them that well.
I do not know a lot about fixed income, options or futures so I will not even try to pretend to explain which one is better to trade. I do know enough to know that they all trade differently. The trading fundamentals are the same but they all have different volatility, volume and risk profiles.
The reality is that most people want to trade too many products poorly instead of focusing on trading one very well. There is nothing wrong with mastering one and then picking up another one. But I can assure you that once you find a way to make money in one of them consistently you will not really want to go through the learning curve of learning to trade another asset class.
I believe all of them offer plenty of opportunities. I prefer to intraday trade US equities because I can always find action in one of the 5000 stocks out there. The learning curve has been extensive enough that I do not see myself wanting to jump into another asset class any time soon. Three years into it I am still trying to get better at trading equities. I do not see how it is possible to trade different products every day without doing them poorly. I tip my hat to you profitable intraday multi-class traders. For those of you ripping it up trying to trade too many things at once please consider sticking to one. Spreading yourself too thin will definitely have a negative impact on your results.