Which is preferable from a functional perspective?

quarter-round1

(defn- quarter-subround
  "### quarter-subround
  A quarter subround.

  Represents a vector of two values:

    [w = (x + y mod 2<sup>32</sup>)
     ((w ^ z) <<< shift)]"
  {:added "0.2.0"}
  [[x y z] shift]
  (let [w (+modw x y)]
    [w (<<< (bit-xor w z) shift)]))

(defn- quarter-round
  "### quarter-round
  quarterround function as defined in [ChaCha Spec][chacha]"
  {:added "0.2.0"}
  [a b c d]
  (let [[a d] (quarter-subround [a b d] 16)
        [c b] (quarter-subround [c d b] 12)
        [a d] (quarter-subround [a b d] 8)
        [c b] (quarter-subround [c d b] 7)]
    [a b c d]))

quarter-round2

(defn- quarter-subround
  "### quarter-subround
  A quarter subround.

  Represents a vector of two values:

    [w = (x + y mod 2<sup>32</sup>)
     ((w ^ z) <<< shift)]"
  {:added "0.2.0"}
  [[a b c d] shift]
  (cond
    (or (= shift 16) (= shift 8)) (let [a (+modw a b)]
                                    [a b c (<<< (bit-xor a d) shift)])
    (or (= shift 12) (= shift 7)) (let [c (+modw c d)]
                                    [a (<<< (bit-xor c b) shift) c d])))

  (defn- quarter-round
    "### quarter-round
    quarterround function as defined in [ChaCha Spec][chacha]"
    {:added "0.2.0"}
    [a b c d]
    (vec (reduce quarter-subround [a b c d] [16 12 8 7])))