HCA Healthcare (HCA) appears an attractive pick, as it has been recently upgraded to a Zacks Rank #1 (Strong Buy). This rating change essentially reflects an upward trend in earnings estimates -- one of the most powerful forces impacting stock prices.A company's changing earnings picture is at the core of the Zacks rating. The system tracks the Zacks Consensus Estimate -- the consensus measure of EPS estimates from the sell-side analysts covering the stock -- for the current and following years.Since a chan ...