Portugal's public system is good and slow, private care is quick and cheap by Western standards, and nearly everyone ends up using both.
Every destination ranking measures cost and climate. The filters that eliminate most options are visa eligibility and whether insurance will cover you at your age.
Every Spanish administrative process needs a bank account and the bank needs your NIE, which is the bottleneck that defines your first month.
Spain's cities differ less than you'd expect on rent and more than you'd expect on tax, because wealth tax is set regionally.
Portugal's national averages are meaningless because Lisbon has detached from the rest of the country, and the gap is now roughly double.
The visa question is answered elsewhere. This is about what daily life is actually like once you are there — the traffic logic, the cash economy, and the parts that take a year to stop noticing.
Most Americans moving to Portugal choose Lisbon by default and a meaningful number regret it. The three options differ more than the guidebooks suggest.
The paperwork is documented and manageable. What catches people is the social and practical texture of the first half year, and it is a fairly predictable arc.