> The US governmental system does have it's issues (first past the post and it's effects being the most glaring), but isn't it the longest continuous democracy alive right now?

Depends how you define it and what you count.

Do you take the union of the English and Scottish parliaments as breaking continuity or not? What do you define as democracy? If some of the population (women, slaves, etc.) are excluded from the electorate is it a true democracy?