P/E ratio for an ETF is much less informative than it is for stocks, because prices are not directly comparable (a ETF with a $20 price is not necessarily "cheaper" than one with a $100 price), and the "Earnings" of a fund are not as simple as they are for the underlying stocks.
Instead, what you focus on is the historical return. ETFs contain hundreds of underlying stocks, so a "share" is not as easy to conceptualize as a share of a company with assets that a shareholder owns a portion of. Instead, a share of an ETF gives the owner a portion of ownership of a massive investment pool. The value of the pool should determine most of the price of the fund, but since the fund shares are traded, they are subject to market forces, and the market might place a premium or discount on the ETF prices for a short time.
You can also look at the historical risk, or amount of swing you might expect in the price of the fund. Like any investment, the higher the risk, the higher the expected return you should expect (since otherwise you'd choose a less risky fund for the same expected return). However, that risk also means that the losses might be higher then other less risky investments.
Finally, look at the fees the funds charge. The fees directly reduce the return, so a fund with higher fees should have higher returns to compensate for the fees.