In which population would you expect disease to spread more quickly?

In an urban area, where there are loads of people „packed” into a small area (like the former Kowloon Walled city in Hong Kong or Hong Kong in general for example).
In poor regions with a high density of people like some regions of India.

In more densely populated urban areas. This is because disease can spread much faster among people who live in close proximity to each other.