I am a futures broker at Cytrade Financial. I personally enjoy trading in the indexes because I have been playing in the stock market since I was in my early teens and have only switched over to futures and futures options as of a year ago.
If I were to choose a commodity that I enjoy trading it would have to be corn. My firm works directly with a lot of farmers from all over the world and we have analysts that have been in the grain markets for 30+ years, so we have a lot of good analysis to base our trades in this market off of.
Agreeing with the other guy above, it is very important that when trading in commodities -- or any investment for that matter -- you have credible, up to date information. That is why I would suggest to anyone without enough time to follow the markets closely to invest with a Commodity Trading Advisor (managed futures). I am building a website right now that has some good information on CTAs and some CTA programs:
www.managedfuturesdepot.com. Be sure to check it out if the above describes you.
Either way you invest in commodities, they are an excellent tool for diversification and profiting in the markets whether it is going up or down. And remember, many 401k plans do allow for investing in futures! I think too many people now-a-days see their investment options as just stocks or bonds.