(when (> x )
    (printf a)
    (return b))

  (cond
    ((> x 3) (printf a)
             (return b))
    ((< x 2) (printf b)
             (return a))
    (t (return c)))

Nobody who works with Lisps thinks in terms of "do I need double parentheses". You just know that if takes two or three expressions, when takes an expression followed by zero or more forms, cond takes a sequence of zero or more clauses which consist of a test followed by a body of zero or more forms.

If you're designing an S-exp syntax for something else, it's probably best to keep the familiar things the same; don't make some different if and such.

The Lisp if maps naturally to the ?: ternary operator; cond, when and unless can compile to cascaded if/else if/else.