It depends.

From times to times I asked or was asked that same question. Technology aside, it's important to consider the skills and expertise that the dev team has. Whether you use language A,B or C or framework X,Y and Z, if your team has a strong background and experience with something make it count too.

I would recommend Go simply because as you mentioned, it's super light. No need to bring in the whole .NET suite to get a simple REST API up and running. Even if your API is a bit complex, Go should be able to handle it.

I started out with C# and .NET and I loved it. In my opinion, it was the perfect way to start learning the fundamentals of software development however I always felt like I was at a disadvantage when I was doing .NET development. Granted, .NET Core is now open-source and cross-platform, but I moved to Node.js simply because it is incredibly popular. I never thought I'd learn to love JavaScript it the way I did with C#, but I learned to love it pretty quickly, especially once I started using TypeScript. You get all of the benefits of C# and JavaScript all in one. If you've built a REST API with Python/Flask/Django, you'll be able to learn Node.js/Express/TypeScript well enough to migrate your API very fast and it's incredibly easy to host for free on any number of services.

I'm new to Go, I've got very little experience but the 'feel' of Go, isn't like Python in my opinion. Go has a pretty steep learning curve, much steeper than C# in my opinion. So if you are willing to consider Node/Express/TypeScript, I think you may really like it. If you're picking between Go and C#, I'd go for C# as of today, but once I am more comfortable with Go (which I anticipate being a slow process) I may change my mind.

At this moment in time, in late 2020- Node/Express/TypeScript feels like the obvious choice to me as a former C# developer.

The best language for you is the one that you know best!

Its a bit of a guess, but from your question and the difficulties you have with Python it seems to me the problem you describe is the manifestation of a bad design/architecture/code quality. These are not the problems of a language itself!

The experience you gained over the past years with your current programming language will outmatch any benefits of another language that you start from zero.

Because in the end of the day languages aren't all that different when it comes to fullfil the same task, it's more the tools, framework and ecosystem for a particular problem that make a difference.

I worked with Java, C#, Go and recently in Phyton, and I would choose Phyton over Go for WebApps, even I like compiled languages more. Go is a very simple language, I would even say maybe too simple. I can't stand all those go boilerplate if err checks, the broken filesystem, the date/time mess and many more things that aren't actually relevant for business application at all. Go has its advantages but not for WebApps.

Keep the lang and improve your skills and architecture you will benifit more from it than from a new language.

I recommend Go for backend. It's younger than C# doesn't mean it's not mature. It's already mature enough to be run on production. You can see there are already many companies in the world adopting Go as their backend business logic or tooling. I can name a few like Github, Shopify, uber, twitch, and many more. It's easier learning curve, low entry barrier, better performance than C#, better memory consumption than C#, since there's no VM/runtime needed. It's suitable for large scale system and large codebase for readibility and long maintainability. It's simpler than C# since no class, inheritance(this can cause hard to maintain software), exception, etc. You can still implement OO way in Go without those feature. Simple file structure, only main files and package files. It compiles to single binary and easy to deploy and work around it, unlike C# who compiled to IL and you need to wrap all those IL files to be run inside separated web server(even .Net/.Net Core platform provide built-in web server). For libs, don't worry, there are many open source libs you will found on Github and already adopted by many companies. Go is employed in personal, startup, even corporate level.

I suggest Go because it has a simple and clean ecosystem. The language is simple. You don’t need complex configs or installs either. You’ll be up and running very quickly. It doesn’t have as much as .NET but its standard library is more than sufficient for RESTful APIs. Concurrency is much, much easier too.

C# I’d definitely recommend later on. The .NET framework, especially core, is extremely powerful and there’s little you can’t build with it. Go won’t take you long to be productive with.

The database your are going to connect and the needed libraries could decide. Because both are awesome languages.

If you want to stick with python you may want to consider Fastapi. It uses Pydantic to give you strongly typed models and validation. It generates openapi docs for you out of the box. They have good documentation as well and they claim it is really fast.

I have some systems on production using both languages. I tend to use golang if the API is small or medium size, but if I am going to build a large system definitively I use c#(asp netcore).

I would recommend C#, particularly Simplify.Web web-framework. C# is easy to start with (especially .NET Core). Simplify.Web is also easy to start with, no extra setup required for simple API, but on the other hand you have power of C# and full control over your API with ability to extend.