ASP.NET Core, it's a great ecosystem with great tooling, and C# is fantastic language to work with. I develop on Windows, deploy to Linux with Docker, docs are great too.
This strongly depends on the purpose...<p><pre><code> How is it sized?
Can it get bigger?
Is it realtime?
Is it Web / App / Other frontend?
What backend languages / tech is supported?
</code></pre>
I always wanted to try or tried successfully:<p><pre><code> SignalR (C#)
Flask (Python)
Gorilla (Golang)
Revel (Golang)
API Platform (PHP)
Hapi (js)
Express (js)
Actix-web (rust)</code></pre>
I've been really happy with express (Node). It has scaled really well for my company.<p>Currently processing almost 200 million requests a month on a cheap $25/mo heroku dyno.