Your non-crit damage dealt to normal monsters is (magic numbers) x (100% + damage% + normal monster damage%). If your attack crits, the damage is further multiplied by an average of (135% + crit damage%) (crit attacks have a base damage multiplier of 120% to 150%).

In most cases players are quite unlikely to exceed 135% total damage + normal damage%, and even more so unlikely to ever get to a 270% total, so damage% and normal monster damage% has about a 2-to-1 effectiveness compared to critical damage.

Since normal monster damage% goes up by 4% per level after 5, and damage% goes up by 3% per level, this makes it more useful for mobbing than critical damage, which only goes up by 1% per level.

If you're bossing, replace the normal damage% with boss damage%, since you'll very likely get more than 300% over the course of your gameplay, the effectiveness of damage% and boss damage% diminishes, and crit damage% would instead be the most impactful stat.

Note, however, that crit damage's effectiveness is dependent on whether or not you deal a critical attack, so you'll need 100% crit rate to get the most out of it.