Clojure works really well for AOC.

A lot of the problems involve manipulating sets and maps, which Clojure makes really straightforward.

I'll second Clojure not just for the data structures but also because of the high level functions the standard library ships with.

Things like `partition`, `cycle` or `repeat` have come in so handy when working with segments of lists or the Conway's Game-of-Life type puzzles.