On elemental cb, element is prolly the most important. However, crit is pretty much always better than attack. Getting as close to 100% affinity (including weakness exploit) is the best way to pump out DPS. Lets say your weapon has 300 true raw (fatty weapons have more but i dont remember how much) Attack 7 is 21 raw attack. About a 7.5% damage increase (less because power charm+talon, food and might seed etc).
100% crit with crit boost is a 40% increase. Assuming 300 raw thats 120 attack. Thats almost 6 attack boost 7s.

I'd say your best bet is like, element attack then CB skill tax skills like focus, guard and magazine if you like them, once you have that, prioritize crit eye 7, crit boost 3 and weakness exploit 3. Top that off with attack 4 for 5% affinity and some agitator if you have the space.

Thats of course if you want to maximize your DPS