Re: the expression:
"Full of (piss|pith) and vinegar"
Are both correct/acceptable? Is one preferred?
There are no appearances of "pith and vinegar" in COCA.
Plotting an Ngram of "piss and vinegar" against "pith and vinegar" shows a similar result; "pith and vinegar" just isn't there. It doesn't mean that "pith and vinegar" is incorrect; it just means that writers prefer to capture the full flavor of the idiom.
(It appears "piss and vinegar" itself is surprisingly recent origin; this source dates its first appearance in the corpus to 1938, in John Steinbeck's "The Grapes of Wrath.")
The OED lists the piss version only. Also, it's far more common on the web. I've never heard the pith version.