It depends. DPShot in this game is never black and white. Though typically Skookum surpasses TumTum on Jakobs for example. It has to with the way damage is calculated. Even on the Hawkeye, where you would initially think more crit is better, if you test them, you will notice a very radical gap in the DPS. Conversely, weapons like the Skullmasher, benefit more from TumTum, which once you understand the damage system, it makes sense. But because crit damage is always based on and applied after your base damage, + damage is superior. Especially because +crit damage needs to hit a crit point to even have any real effect. +DMG is obviously always in effect, so even if you mess up, youre still gaining the benefits.
What is a man?! A miserable little pile of secrets!