Depends on how you trade, if you are a frequent trader then IB are great but as most commodities trade in the US you better get used to being a night owl if your in Australia or NZ although quite a few have long trading hours but beware when out of the main day/pit session as volume drys up and spreads can blow out in some markets.
MF Global are good if you want to position trade and although you pay more in brokerage you can sleep at night without worrying if an online platform has executed your orders.
Also contract size in some of the big liquid markets is big, Crude Oil for example is US$1000 per big point or US$1 move, there are mini contracts but volumes are much lower although Crude isn't too bad.