Exchange Traded Funds or ETFs are definitely my investing/trading instrument of choice. I like them for a number of reasons.
First, they pretty much cover any area of the market. There are industry specialty funds for healthcare, housing, technology, commodities, etc. There are also ETFs that cover indexes for a broader exposure to the market.
Second, they have bearish funds which let you get short the market and not have to pay margin interest. As the industry stands now, you have to see if a stock is marginable and if there are shares to short from your broker dealer. Then you have to pay margin interest to your broker dealer who has borrowed the shares on your behalf. This does not exist in bearish ETFs, you can short the market without any additional cost.
Third, they have leveraged funds. These funds essentially give you a high beta investing (trading) option without having to borrow money from your broker/dealer and where you would again pay margin interest. I would not recommend these for the faint of heart and most ETF companies will tell you that these instruments are made to be trading vehicles only and not meant to be held long term.
Fourth, they trade like a stock. One of the things that drove me crazy when I worked with mutual funds was that you could only tranact at the end of the day. So if the market turned and headed south there was not much you could do. Not so with this investment class.