Which commodity futures are best for day trading?

Although it's not a commodity in the traditional sense, e-mini contract futures has worked the best for me in terms of your two requirements (predictability and liquidity). The E-Mini is regulated and has the same players, day to day. Floor traders (open outcry) and financial institutions trade it for a reason. When trading the emini, watch out for news events that can make price rise or fall rapidly. Most of the time, it's best not to trade when planned U.S. news events are announced.