stat

is 20 cd% = 20% stronger against ele ?
and cd% and atk% which one better ?

 

20% critical damage is better than both.
it multiplies the critical damage multiplier by 1,2.
the critical damage multiplier is 1,5 (150) and it increases by 0,01 (1) for every 5 STR points.
even without STR, 20% critical damage will raise the multiplier to 1,8 (180).

20% against element will multiply your damage by 1,2. that's the same power as critical damage +20.
critical damage +20% equals critical damage +30 (more if you raise STR).

atk% multiplies your base atk. this is NOT the number you see on the stat screen.
the stat screen shows your total atk.

critical damage % is better than atk%, IF you land a critical hit.

 

While this is right, keep in mind that +20 CD% is different from flat +20 CD.

Your actual question must be between flat CD and %damage to ele since 20 CD% is pretty much impossible to have in one piece of gear (with CD% cap is only +10). And, the short answer is %damage to ele giving higher damage compared to flat CD