Pampa Energia (PAM) appears an attractive pick, as it has been recently upgraded to a Zacks Rank #2 (Buy). This rating change essentially reflects an upward trend in earnings estimates -- one of the most powerful forces impacting stock prices.The Zacks rating relies solely on a company's changing earnings picture. It tracks EPS estimates for the current and following years from the sell-side analysts covering the stock through a consensus measure -- the Zacks Consensus Estimate.Individual investors often fi ...