As josh said options will always give you the greatest leverage, but you need to understand how to trade them first.
The benefit of /ES is that you can trade it 24 hours a day contrary to options and SPY.

Here is a link to an Al Brooks article on the subject:
Brooks Price Action - Daytrading ETFs and Stocks

Bookworm 

Here is a link to an Al Brooks article on the subject: Brooks Price Action - Daytrading ETFs and Stocks

The article is missing, appears they all are on Al's site.

EDIT: It appears you need to be logged in on his site to view it. Duh.