RE: in your opinion, the best deer hunting caliber...
Caliber is basically the bore size which has very little effect on accuracy or flatness of trajectory.The cartridge designation describes both the caliber and shell casing which is what really decides the velocity potential.The velocity and ballistic co-efficient decide the trajectory of the round.The accuracy of a gun is decided by the quality of the barrel,bedding,trueness of the action and the suitability of the ammunition for the gun.There are many suitable cartridges and rifles available but if accuracy and flat shooting are your primary concern I would consider such rifles as the remington sendero in chamberings such as the 25-06,7mmrem mag or 7mmstw.