My two favorite languages were both developed by Microsoft and Anders Hejlsberg: TypeScript and C#, in that order (honorable mention to PowerShell). Both are incredibly well-designed languages with these features in particular that I love:
I've been doing more and more programming in Node recently. I've also had to work with a couple of Java programs in there, and I've realized how valuable having first class support for async logic is. C# introduced the world to async-await, and JavaScript/Node excel at async logic probably better than any other platform. And TypeScript adding type support to JavaScript actually makes JavaScript a useful language for large projects. And while TypeScript/JavaScript is not exactly a pure functional language, I do enjoy what parts of FP that I can do with them.
My least favorite language, mostly for superficial reasons, is Python. I think making whitespace meaningful is stupid, and generally I dislike any language that uses snakecase as a language convention (i.e. underscores in variables). It's inconvenient to type and hard to read. And also think dynamic languages are undisciplined and sloppy. TypeScript is the only reason that I enjoy working with a dynamic language; I get all of the flexibility of a dynamic language and all of the safety of a statically typed language.