I love
Frederick I'd really like to use it one day, either on it's own or as a middle name (
Charles Frederick is one of my top combos).
I would use
Fred or
Freddie but I don't think it is inevitable. I knew an
Alexander who only went by
Alexander and that is similar in length to
Frederick.
Federico is nice but I think I would mistake it as
FRederico a lot but that wouldn't apply everywhere.