Best and Worst Performing S&P 500 Stocks Year-to-Date. May 22, 2015. For those looking to catch up on 2015’s winners and losers over the long Memorial Day weekend, below is a list of the 40 best and worst performing stocks in the S&P 500 YTD. As shown, Netflix (NFLX) tops the list of winners with a gain of 82.68%, followed by Skyworks (SWKS) at 45.26% and Hospira (HSP) at 43.98%.