Aussie Flag or US Flag on Vessel ?

[AllezCat]

Hi All,
I am an American and Australian citizen. But, primarily live in New York.
I intend to purchase a vessel soon. And live-aboard in NYC, Florida/East Coast with some offshore to Canada and Bahamas within the first year.
I just want to pick the best flag to avoid hassles/fees.
Some have suggested I Aussie flag it and get a 1 year cruising permit for USA.
If a vessel currently has British flag and VAT paid - then re-flagged as Aussie or USA , does the VAT remain for the next(European) owner?
What are the experiences and opinions?
Cheers