What do you prefer in Back-End development? (Not games' servers with APIs and etc.)

What language? What framework? And why?

.NET Core
Because I am familiar with C# and the code can be ported to Linux without using Mono

I've also done a lot with .NET (MVC).

Been working for little bit over 2 years in Spring framework for Java. It's de facto standard for developing strong enteprise apps in the Java world.
I'd like to take a look into Go lang though.

I am using PHP and Laravel. Why? Because Laravel gives elegance to a powerful language that is a bit.... chaotic. I know it souns kinda cliché bit it really works.

I am currently moving over to Go/Rust for my backends, though I previously used PHP and Laravel/Lumens for many years. I have used node.js for a few projects that required a simple api.

For Go, I find Mux is a really nice routing system, with all the benefits of a modern language.
and for Rust I am playing around with Rocket, which again is a really fun http framework to use, with the benefits of being a modern language and having the speeds of something similar to C++.

For my frontends, I use Javascript with Svelte or ReactJS. Though recently have been playing around with next.js, which is a similar yet fun framework.

I study a couple of frameworks though.

If I want fast development without concerning the speed and readability of the code and processes I use C.I 3 with HMVC plugin by wiredesignz. It's easy to understand too and making a backend system is fast, security wise is bad.

If I want a slow development concerning security, speed and readability of code and processes I use Laravel, just pure laravel because I haven't heard of Laravel/Lumens before today. A lot of learning curve for this one but hey if you want a much more secure PHP framework well Laravel is good for you.

Finally my new friend and buddy, Python Django, but I only use this guy if I want a full on Statistics website, such as an admin website that needs a lot of graphs and calculations, although I also use python as a library on Laravel and C.I 3, it's much faster when it's done in Django, I don't use Django without Numpy by the way.