Answer: sincerest

AnswerCrossword Clue
SINCERESTImitation's rank as a form of flattery
SINCERESTMost heartfelt.
SINCERESTMost deeply felt
sincerestFree from pretense or deceit; proceeding from genuine feelings
sincerestSINCERE, genuine (authentic)
sincerest(of a person) Saying what they genuinely feel or believe; not dishonest or hypocritical