Depends on range.
Heavier bullet keeps momentum at distance, higher velocity at any given longer range.
Short range it doesn't much matter, the lighter bullet won't drop to trans-sonic or sub-sonic.
Lots of guys shoot light bullets very accurately at shorter ranges, see varmint bullets...
Given the same muzzle velocity, same wind resistance/ballistic coefficient, a heavier bullet will maintain momentum better.
Out here where we can shoot longer distances, when a guy is shooting MOA out to about 600-800 yards,
The rifle/round will do MOA out to a certain distance, then the group will suddenly spread out.
This is the limit of the bullet being used, where it starts to yaw in flight.
The lighter the bullet, the sooner it looses momentum to wind resistance.
This is discounting internal ballistics, the rifling twist rate, the depth, width, number of rifling lands/grooves, overall diameter of the bore, etc.
Most of us try several different weights, slightly different diameters of bullets to find out what works best with the rifling.
I always go with a heavier grain bullet for accuracy and consistency, long or short range no matter the twist rate. That decision has worked great for me so far..
I have pretty much moved to 175gr because of the heavier bullet that gives better resistance to wind, more retained energy and a smidge more accurate. The 168gr ammo is still good to go though in my opinion. Lot's of veteran snipers went their whole career using 168's just fine so it's hard to argue they aren't a viable option, it's just that the 175's are a bit better in those same areas.