"When you have written your headline, you have spent eighty cents out of your dollar.”
~ David Ogilvy.
Headlines are critically important, yet it's impossible to know in advance which headline works best. Hence you need to test which resonates best with your audience.
Finding best headlines via statistically significant PPC split tests takes you about a week and a ~$1000. Copytesting gives you results in hours, in under $100.
Find the headline that piques interest, get more customers.