Depends, what are you looking for? Burst damage or DPS?
Double Blow has 2sec cooldown so would give you more DPS in the long run.
Crippler does a big hit (burst), and has a high ch-atk added aswell, but comes with a very long cooldown (9seconds).
Basing it on lvl1 skills (and my gear etc):
- Crippler 809-1165 dmg / 218-498 ch-atk
- Double Blow 644-925 dmg / 112-282 ch-atk
Taking the high-end dmg of both skills, the dps is:
- Crippler 1165+498/9 = 184,77 DPS
- Double Blow 925+282/2 = 603,5 DPS
So, to out-DPS Double Blow, Crippler needs to have 3,3 times the skill damage of Double Blow. To maximize DPS, a balance between the two skills should be the best solution.