We started out core product on ECS, which is a declarative way to run a containerized service. It has been nice and reliable, but it has limitations (slow scaling, weird AWS Quotas if you have ephemeral tasks).

We're moving our non-critical components onto EKS (pipelines, tooling, etc). We had one outage from runaway IP allocation in a subnet, but otherwise it's been pretty stable.

I do hear vague horror stories so I'm really not excited about moving our prod stack to it, but it's actually been really good for installing 3rd party software so far.