Billionaire Ken Griffin has been buying Palantir stock and selling shares of Nvidia this year, but investors may want to do the opposite.Shares of Palantir Technologies (PLTR 0.63%) and Nvidia (NVDA 2.25%) have skyrocketed 223% and 194%, respectively, this year, as of Nov. 6 amid strong demand for artificial intelligence (AI). That makes them the second-best and third-best performing members of the S&P 500 behind electric utility Vistra.Interestingly, Ken Griffin's Citadel, the most profitable hedge fund in ...