Definitely New Zealand. Absolutely not America. I don't really think you can comment on the UK if you've never stepped foot out of your country though.
New Zealand, Iceland, Australia, French Polynesia (technically ecuador) are top tier. Not quite top tier but also very liveable countries are Japan, Malaysia, Norway, Canada, Dominican Republic, Argentina, Mauritius.
Honestly the USA is a good country if you live in a place with a good community and isn't overly political.