I would second the 85 Sierra vote! Have used this bullet for years in both the .243 and the 6MM-284. It is not only a good varmint bullet, but works very well on deer sized game. One of my companions shot a cow elk last year with this bullet in the 6MM-284 - went down in about 5 seconds from a lung shot.

Another real sleeper all-around bullet in this caliber is the 87 grain Hornady Spire Point. I never got quite as good accuracy as with the Sierra, but the terminal performance is great.