Personally, I always saw Mew as a female since it looks and sounds very feminine to me. Also, in Pokemon Blue, Pokemon Red, and Pokemon Yellow, some journals a dit that Mew gave birth to Mewtwo, and thus, that means it must be a female.
So, yeah, I always see Mew as a girl, unless its shiny.
Mew is a species, not an individual. Since the gender ratio of the Mew species is a dit to be “unknown,” it's unclear whether male and female Mews both exist, ou if they're a female-only species. It could be like the Miltank species, only having females ou like the Tauros species only having males. Personally, I thought that Mew sounded like a female because of it's voice. But then again, Ash's voice sounded sorta like a female's, yet he was a male. So Mew can be an only male species, only female species, ou a genderless species, and the answer will remain unknown until further notice.
