I've been on C# for over a decade and I'm still very happy with it. I think it's highly underrated in the startup space.

When helping start my current startup, one of the founders asked why I chose C# as he was asked by others why we'd pick that language/stack as it's not common for SF startups. I told him that it's less about the language and I could do just about anything with it. It's turned out great and of all the things to worry about, the language hasn't ever come up again.