Liquidity and slippage(trading on Island) are both very good.
The two biggest differences are:
1. Futures offers much better tax advantages.
2. Commission savings: An example would be if you
were trading the QQQ,s and paying 1 cent per share
for 1000 shares, you would pay $20.00 for the trade.
Trading 1 contract on the Nasdaq E-mini would cost
about $5.00.