Since it's been an hour and there hasn't been much response, I'll give my two cents.
I don't work for a startup. However, I do work in a small team of 3 developers, and have recently been faced with the decision of choosing a technology stack to start from scratch.
Before this decision, we were using PHP5; we were constantly putting out fires and couldn't ever get any actual work done because of this awful inherited codebase.
WARNING: OPINIONS AHEAD.
We decided to not go the .NET route for a few reasons.
Object-Oriented programming doesn't have a place in our hearts, as it does with a many OO-only developers. I find that object-oriented code is overly verbose and often difficult to maintain. For these reasons, we also wanted to avoid PHP, Java, and node.js. I feel like object oriented programming is more of an obstacle I have to overcome than a feature.
I hate to say it, but I just don't trust Microsoft. Yes, .NET on Linux is incredibly fast. How many years down the road until Microsoft decides to try getting their new Linux user-base onto Windows? They've done similar things before, and it'll take more than a year of a "Microsoft Not only that, but .NET core hasn't been on Linux for a very long time. There isn't as much documentation that I can find on running, deploying, and maintaining a .NET / Linux application as many other technologies. (note: I could be wrong here after some more research, it's been out for a couple years, which is probably enough time).
We decided to go with Golang. It's a statically typed language that treats functions as first class citizens. It's not object oriented, doesn't have exceptions (yay), has an amazing standard library (including testing and benchmarking!), is easy to deploy (compiled & doesn't depend on a runtime like JVM or .NET core), and I feel like it's working with me, not against me. Plus half of our stack is already in Go (docker & kubernetes, and now Tyk).
I know that so many of you will absolutely disagree with me and that's fine. I'm not here to start fights, just giving my two cents. :)