Which STALKER game is the best?

Of the three S.T.A.L.K.E.R. games (SoC, CS and CoP) which one did you think is best, if you played all of them. I've completed only Shadow of Chernobyl and Clear Sky so far, and I must say that SoC is probably the superior one. However, Clear Sky's gameplay was slightly better and the equipment mods are awesome. In the end, I can't vote until I have played CoP. Which one is your favourite?