Seyfried had her commercial breakthrough in 2004's Mean Girls, in which she played the ditzy and impressionable Karen Smith.
Speaking to IndieWire, the actress said she is eternally grateful to have starred opposite Lindsay Lohan and Rachel McAdams in the Tina Fey-written film.
"I was so innocent. I was so green," Seyfried recalled. "I still look back at Mean Girls as my best work."
[Amanda Seyfried, Lindsay Lohan and Lacey Chabert in 'Mean Girls']
She further explained: "I look back and I'm like, 'Really, I thought I was doing a terrible job'. But it was written so well and so wonderfully directed.
"[Director] Mark Waters made me look good; he made me funny. And Tina Fey wrote the coolest script of all time."
Seyfried's success in Mean Girls led to her role in the critically-acclaimed polygamy-themed HBO series Big Love.
She ultimately branched out into films in projects such as Mamma Mia!, Dear John, In Time and most recently Les Misérables.
The actress next appears with Robert De Niro, Diane Keaton and Topher Grace in the comedy The Big Wedding, opening on April 26 in the US and May 31 in the US.
Watch a trailer for The Big Wedding below: