The long or short version?

[Ginger]

i think if you want him to be called Olly, then that's what you should call him. if you call him Oliver then people will call him Oliver. will that annoy you?
we went through this issue when naming ds2 and decided in the end to call him the 'nickname' as his fullname, as that's what we wanted his name to be and didn't want to be conservative just to please others.