[4pkjai]

Kotlin, because it’s a language I like

[jpgvm]

IMO it's maybe the best suited language to AoC. You can write it even faster than Python, has a very terse syntax and great numerical performance for the few challenges where that matters.

[ilvez]

I know this is pretty personal but Python's way with indention really does not play well with throwing things out. It's obviously matter of practice, but languages that have same qualities but are easier on formatting issues and aren't that set on one correct way of writing things allow much doing things much faster. But at the end, it's personal :-)

[speed_spread]

Modern straight Java works just as well.