"This is the best gift!"
Translation:¡Este es el mejor regalo!
Esto is neither masculine nor feminine. It is a neutral pronoun used (1) when you can't know the gender of the object: ¿Qué es esto? What is this?; or (2) when you are referring to a situation or set of circumstances: Esto es terrible. This is terrible.
Since we're saying "This (gift) is the best gift," we make "este" masculine to agree with "regalo."