Alas, if you consider Sydney winters too cold to bear, then you'll probably have a bad time in Lisbon too.
Sydney is not only warmer on average, but also much less prone to cold spells (not that cold spells are common in Lisbon, but they certainly occur more frequently: the last time it snowed in Sydney was 1836; the last time it snowed in Lisbon was 2006).
I think the climate you're looking for is more in line with Miami.
It's true but I'm happy to trade some climate for the other factors on my wish list. Sydney and Melbourne both fail not only on climate, they're also not as diverse and cultured and don't have super great public and alternative transport. Based on the feedback here Lisboa def seems like a top option. (by all means Miami too)
Sydney is not only warmer on average, but also much less prone to cold spells (not that cold spells are common in Lisbon, but they certainly occur more frequently: the last time it snowed in Sydney was 1836; the last time it snowed in Lisbon was 2006).
I think the climate you're looking for is more in line with Miami.