Where you already have some Chef recipes to build your application boxes and are happy to run directly on VMs, OpsWorks really shines. It won't do anything too complex for you, so it only really works well for simple stacks (load balancers, application layers, database layers). If you want to do more complex infrastructure, Cloudformation or Terraform are probably worth looking at.
TeamCity is very quick and straightforward to get up and running. A new server and a handful of agents could be brought online in easily under an hour. The professional tier is completely free, full-featured, and offers a huge amount of growth potential. TeamCity does exceptionally well in a small-scale business or enterprise setting.
Getting up and running with OpsWorks is a very technical and potentially time-consuming process. You need to know the ins and outs of Chef/Puppet if you really want to get into it and there isn't a convenient way to test out the environment locally so debugging can be time-consuming.
To take advantage of some of the newer AWS instance types you need to be running on a VPC, which again is a pain if you don't have a DevOps team.
The error logs and monitoring metrics in OpsWorks are pretty basic and haven't changed much over the years.
The customization is still fairly complex and is best managed by a dev support team. There is great flexibility, but with flexibility comes responsibility. It isn't always obvious to a developer how to make simple customizations.
Sometimes the process for dealing with errors in the process isn't obvious. Some paths to rerunning steps redo dependencies unnecessarily while other paths that don't are less obvious.
TeamCity runs really well, even when sharing a small instance with other applications. The user interface adequately conveys important information without being overly bloated, and it is snappy. There isn't any significant overhead to build agents or unit test runners that we have measured.
Unless you pay for a pricey support package getting support on OpsWorks will be pretty slow. Documentation is also relatively limited and sometimes hard to follow when compared to competitors. Generally, we've been able to get the answers we need from OpsWorks support when we run into problems but don't expect rapid responses.
OpsWorks isn't really a direct competitor to Terraform/Cloudformation, but it does allow you to do some of the more simple things on offer quite quickly and effectively. Opsworks was used for this reason, along with existing internal knowledge of Chef. Along with some of the other services on offer from AWS, it is good to use as a stepping stone along the way when building your systems - or perhaps it would be entirely suitable for a fairly simple project.
TeamCity is a great on-premise Continuous Integration tool. Visual Studio Team Services (VSTS) is a hosted SAAS application in Microsoft's Cloud. VSTS is a Source Code Repository, Build and Release System, and Agile Project Management Platform - whereas TeamCity is a Build and Release System only. TeamCity's interface is easier to use than VSTS, and neither have a great deployment pipeline solution. But VSTS's natural integration with Microsoft products, Microsoft's Cloud, Integration with Azure Active Directory, and free, private, Source Code repository - offer additional features and capabilities not available with Team City alone.
TeamCity has greatly improved team efficiency by streamlining our production and pre-production pipelines. We moved to TeamCity after seeing other teams have more success with it than we had with other tools.
TeamCity has helped the reliability of our product by easily allowing us to integrate unit testing, as well as full integration testing. This was not possible with other tools given our corporate firewall.
TeamCity's ability to include Docker containers in the pipeline steps has been crucial in improving our efficiency and reliability.
