'Hold it' is both colloquial and aggressive - it sounds a bit angry.' 'Wait' is a neutral word - it's neither polite or impolite, it's the regular way to convey this idea. :)

There's no difference between them

Hi Ensomih, Hold it is slang and should only be used with people that you know well. (It could be considered rude.) Please wait would be correct for people that you don't know well. Stop! or Wait! would be used if someone were in danger or some other extreme situations Sue