us-east-1 is where they typically deploy new features/hardware first (with the exception of efs which went to us-west first for some reason). it's also by far the largest region, with the most tenants and the heaviest traffic, so it's approaching the limit on what's physically possible to do in a public data center.
It's the primary AWS region. You spin up your resources by default there unless you explicitly select another region in the console.
It's probably a good idea to pick other regions, especially the ones closest to yourself
However, us-east is usually the cheapest one as well