Just read them back to back, regulators last. Feel that Regulators is a story of the "random" vs desperation the "purpose". Desperation is the story that was pre destined or of gods will. Regulators is the random luck of the perfect vessel for tak coming within its range.
I enjoyed both but Desperation more as I was more invested in the characters.
What sticks with me is wondering how many of the strings Seth was pulling in the regulators and how much of the terror that was unleashed was taks design vs Seth allowing it to play out that way so he could get the ending he desired.