Please provide your regarded opinion

In my keeper fantasy league, I have 5 of the greatest starting pitchers, but can only keep 4 players for next year.  Basically, I need to choose one of the following to leave by the wayside: Johan Santana, Francisco Liriano, Ben Sheets, Chris Carpenter, or Rich Harden.

The league is points-based, with outs and K's worth +1, and all baserunners, earned runs, and other bad things worth -1.  Wins worth +10, CGs worth 5, and SHO worth 10.

Now, the Twins are safe, let's get that out of the way.  My main decision is between Sheets, Carpenter, and Harden.  Sheets and Carpenter have an easier time in the National League, with easier lineups and free strikeouts via the pitchers.  Harden has missed huge stretches of the last two years with injuries, but is young and has great upside, though he is at a disadvantage because of the DH.

So, please opine on this situation.  I will leave a poll slot open for the possibility of trading two of these fine pitchers for one marquee slugger, and keeping 3 pitchers and 1 hitter, which may be a better plan.