If you have enough substats on other gears to rate up your crit chance or use up to 3 crit sets its recommended. Or you pray to RNG and have either a normal hit or one that really hurts - chance of that is crit chance. So:be save and do always for ex. 150% attk value hits or have sometimes 100% but then maybe 200%.... your decision. Its some kind of calculation whats the best effort.

The same is the decision if you use atk or dest. set - if your crit chance is low, than an attack set is better, because it takes effect every time, with better crit chance destr. set can be better....

but at the end: it is how RNG likes you or not...

You could calculate the average you could expect from your atk, crit rate and crit dmg. For example you're comparing two sets:

Set 1 (crit chance neck):
3000 atk
100% crit chance
190% crit damage

(3000 x 1.00 x 1.90) = 5700

Set 2 (crit damage neck):
3000 atk
70% crit chance
260% crit damage

(3000 x 0.70 x 2.60) = 5460

In this case, set 1 is better and more reliable. Of course, depending on your own gear, the results may vary if you have better sub rolls.

thats wrong.... you have a 70% chance to get either a 3000 attack or a 7800 attack...

If you like to calculate that exactly you can use a damage calculator, like:

https://maphe.github.io/e7-damage-calc/

I agree with sirwerner that blu's math is wrong, although how he phrased the reasoning is not clear even though it is correct

The issue is that you have 70% chance to deal 3k*2.6=7.8k and a 30% chance to deal 3k so the math is (3k*.3) +(7.8k*.7)=6360 as the weighted average.

For the original question the actual stats is what really matters so a good attack set can beat a decent crit dmg set. Crit dmg set in general is superior assuming perfect rolls. There are a few technical scenarios that should be considered tho attack set will give you more minimum damage in case of misses and non crits. Some debuffs and artifacts like Burn/bleed/uberius tooth/reingar special drink scale directly off attack only.  Skills and artifacts that scale off the enemies max hp are also affected by crit dmg. For average damage optimization just follow sirwerners link.