Neither. The question is based on a false premise alltogether - there is no evidence that legalization in any way correlates with increased trafficking, even the people making the claims are forced to acknowledge that.
I addressed that earlier on Skeptics.SE: even the vocal proponents of the theory have zero data to back them up:
Yet they quickly add that no statistics have ever been gathered and law enforcers never before have made it a top priority - so the scope of the problem still needs to be determined.
... The task force's first task was to determine whether, in fact, there was a human-trafficking problem, Lesney says. But because of the lack of hard data, she says, "we were struggling to quantify what we're dealing with."
Basically, they have no evidence that there's widespread trafficking in the first place; never mind that it has any relationship with legalization of sex work in Nevada (as it admits that the trafficking numbers that are known include general labour workers). There are almost no arrests/convictions for this, the article listed 9 cases in last 6 years, despite having tough laws on the books.
A separate related Q&A on Skeptics looked at Netherlands. While it didn't directly address the question, the numbers cited show that between 1.5% and (at the highest possible estimate) 6% of sex workers in Netherlands (between 450 and 900 out of 15-30k) are trafficking victims. For comparison, Belgium, which has no legalization, had at least 500 victims in the same period, and since the number is merely those who had help from NGOs, real number is likely at least as high as Netherlands - while the population of Netherlands is 50% higher than of Belgium (11M vs 17M).