What batting traits make a good baseball or softball hitter?
There are many traits that great baseball and softball batters share.  Some of the most important are extreme confidence, sound batting mechanics, and coordination developed though a combination of talent and practice.  

All great hitters share some consistencies in their batting mechanics such as their lower half mechanics, their hand and bat path, and their head and eye movement.

With their lower half mechanics they generate powerful torque from the ground up by timing the planting their feet in a balanced position and forcefully rotating and opening their hips.  Hitting powerful line drives relies heavily on the barrel of the bat meeting the ball flush.  Batters increase the odds of this by keeping their hands in, connected to the back shoulder, and having one palm facing up and one palm facing down for as long as possible as the bat path travels through the strike zone.  Finally, all great hitters maintain consistent head and eye position throughout the motion. 

There are many nuances of batting mechanics that all great hitters share but these are some of the most important.