NEW YORK ( TheStreet) -- Risk-adjusted returns are often the most important gauge of exchange traded funds.The following five ETFs earned TheStreet.com Ratings' highest rank of A-plus, or excellent, for risk-adjusted returns over the year ending Jan. 31, but also rated well in so-called structural-integrity factors such as expense ratio, bid/ask spread, tracking error, market impact and efficiency. First Trust Mid Cap Core AlphaDEX ( FNX) rose 47% and ranked in the 56th percentile of structural integrity, according to Marco Polo XTF. The fund's three best structural accomplishments are low tracking error and concentration risk, and high efficiency. By maintaining a six-month tracking error of just 0.32% to the price-and-yield performance of its underlying benchmark, the S&P Defined Mid Cap Core Index, the ETF ranks in the 62nd percentile for tracking error. XTF.com places the fund in the 88th percentile for concentration risk on low individual constituent weightings and high number of holdings, preventing over-exposure to individual stocks. An efficiency ranking of 86% shows the fund managers' ability to generate alpha, returns in excess of its benchmark, with stock selections like Barnes & Noble ( BKS), Ralcorp Holdings ( RAH) and Patriot Coal ( PCX). First Trust Health Care AlphaDEX ( FXH) also did well, with low tracking error and concentration risk. On top of this, the ETF ranks in the 59th percentile for average bid/ask ratio. The smaller the average spread between the bid price and the ask price, the more attractive the security becomes to traders. Tightening bid/ask ratios show a fund becoming more popular as average daily trading volumes increase. The fund is seeking healthy returns from UnitedHealth Group ( UNH), Tenet Healthcare ( THC) and Humana ( HUM).