I like the Aayala Secura thought. She, like Boba Fett came from EU to the movies.
Jango Fett is the obvious answer, yet he's not.
Maul was popular, but not in the Boba sense. He was more of the Vader replacement for TPM. I think part of the problem was that there were too many attempts to have a Boba Fett in the PT. We had Aurra Sing, Zam, Jango, and a lot of other minor characters who were pushed to be made poplular.