Ask HN: Launch On-demand startup in small town or large city?

Hi HN,

Let's say I was interested in launching an on-demand startup in a new market.

Should I launch in:

a) A large city, population 1M+, to have the opportunity to grow as fast as possible?

b) A smaller town, population ~50,000, to be able to validate my assumptions and improve my product before I launch in my largest target market?

Cheers