You want a little bit of 'preload' but my experience has been that the times I've erred on the tight side have been when I've later gotten the 'indexed steering' problem where there are tiny depressions in the bearing race and the balls tend to fall into them - i.e. preferring the straight-ahead orientation. One explanation for the depressions is that if the lubricant is squeezed out of the ball-to-race interface and you're going straight on a rough surface the vibrations can lead to fretting of the race at the contact of the ball.