To me, a nickname is a nickname. I love the name
Alistair - which screams masculinity to me - but the most obvious nickname is
Ali (pron.
Allie), which I would undoubtedly say.
If you were hoping for a stronger nickname,
Sonny is always an option. Emers is a neat one, but to me, it would take practice to say that as a first response.
Em would be the first short form out of my mouth.
I also see
Mercy as a nickname for
Emerson, but that leans feminine to me.