Damage tech is better; aim tech is only better for long-range weapons. As I understand it, it only increases damage by 10-15%.
It could be more, but weapons have a range limit.
Just to be clear aim tech doesnt increase dmg by %.
I have done testing with aim attribute recently and aim clothes set adds nearly the same amount of damage per shot as damage clothes set, but its only like that at 55 lvl yager range + 55 lvl range tech.
Also keep in mind that if aim adds lets say 2k damage to the shot, then it will also add 2k to the skill damage, not like its with damage attribute which increases weapon skill damage proportionally based on % written in skill description.
Based on my experience I would also agree that its better to use aim on weapons with far range and will add that its better to use aim on weapons which have low weapon damage attribute, in other words on pm, colt and gatling.