It looked at three major components elements of an ETF: annual expense ratio, the securities lending revenue, and trading spread.
The first one - annual expense ratio is a conventional one, as the main draw of ETF is its super low expense.
The second element is interesting - for some ETFs, especially the ones holding shares in small or international companies, they can lend the stocks to investors who want to short the stocks and profit from the lending. In fact, a few ETF's even have negative cost of ownership!
The third element is important for swing traders.
What are the best ETFs? It depends on which categories you are looking for. For example, the best diversified large cap ETF's are VTI, SCHX, and VOD. The best small company ETFs are VBK, VB, and IWM.
You can see the results here.