Also, I really dislike the nn
Nick /
Nicky. I would prefer to see
Dominic and
Nicholas used in their full form. However, if the nn is a must, I would have to say
Dominic, because
Nick is a different nn than expected (most would expect
Dom or something of that sort). But if you are one that doesnt like conflicts with a name (always saying "my name is
Nick, short for
Dominic, not
Nicholas"), I'd go with
Nicholas.
I love both names, and in general, I'd like to hear more
Dominic's out there (but I'd also love to hear more
Nicholas' using their full name)