I am a big advocate of the .220 Swift.  I love this cartridge.  My Ruger Target rifle shoots 1/8 MOA and 100 yards off sand bags with factory Hornady V-Max's and I have shrunk the groups a little with alot of tedious handloading.  The .22-250 is another great choice.  These are serious long range varmint cartridges.  My Swift drops coyotes at 400 yards with authority.  The .223 is a good round, but for long distance the large centerfires take alot of the guess work out of trajectory.  I haven't shot a .223 WSSM, and I have no need for one (the other two are just as good and easdier to find rounds for).  If you are into reloading, the .243 Win is a good choice, it will launch heavier bullets around .22-250 velocities.  [/img]