#2 Why Roman Reigns is better as a face: Being an inspiration to the fans
Roman Reigns was often compared to multi-time world champion John Cena in the past due to Vince McMahon's refusal to turn both stars heel. Most wrestling pundits wanted the change because they felt that their characters became stale and a heel turn was the best solution.
While John Cena becoming a bad guy could've been awesome, it would've been an issue due to Cena's popularity with the younger audience, which is the demographic WWE's product is targeted at. The younger fans look up to The Cenation Leader and consider him to be a role model.
Cena is also considered to be a hero due to his Make-A-Wish contributions. If he had to heel, it would shatter the hearts of millions of children. That's why John Cena was best suited as a babyface. Although Roman Reigns was constantly booed and criticized by the hardcore fans, he was still immensely over with the younger audience.
That's one of the reasons he was chosen to succeed John Cena as the face of WWE. Many people looked up to Roman Reigns as their hero when he was a babyface. It's hard not to, especially after he defeated cancer twice and came back healthier and stronger, which inspired a lot of people and it's something he can only do as a babyface.
#1 Why Roman Reigns is better as a heel: He will get the desired crowd reactions
WWE's refusal to turn Roman Reigns heel several years ago was met with a lot of backlash from fans and critics. It became so bad that they started piping in and editing crowd reactions to remove the chorus of boos Roman Reigns was receiving and replacing it with cheers.
No matter how hard WWE tried, the fans just wouldn't accept him as a babyface. Now that Roman Reigns is finally a heel, getting booed will actually work in his favor instead of against it. With live crowds set to return very soon, Roman Reigns will get the desired crowd reactions which will be perfect for his character.