I like to use Haskell, because parser combinators usually make the input parsing aspect of the puzzles extremely straightforward. In addition, the focus of the language on laziness and recursion can lead to some very concise yet idiomatic solutions.

Example: find the first example for when this "game of life" variant has more than 1000 cells in the "alive" state.

Solution: generate infinite list of all states and iterate over them until you find one with >= 1000 alive cells.

    let allStates = iterate nextState beginState # infinite list of consecutive solutions
    let solution = head $ dropWhile (\currentState -> numAliveCells currentState < 1000) allStates