Mr. WebLog explains the whole stuff here ... http://highprobability.blogspot.com/2007/06/best-broker-for-trading-futures-based.html
You can compare unbundled to bundled here: http://www.interactivebrokers.com/en/accounts/fees/futuresPricing2.php?ib_entity=llc Unbundled is a few cents cheaper but does not include the 10 cent per contract carrying fee charge. So if you only day trade and are flat by the end of the day then going with the unbundled package is a bit better.