Well it is certainty safe. If partner has a black ace(or any ♠ entry), club is right. If partner has a red ace, then you want to setup a trick in a 2nd suit before they can set up pitches for it. Hearts are out cause you are to likely to give up a trick with the lead. Diamonds are awful likely to find one of the opponents short enough so setting up a trick isn't even an issue. It is possible diamond is the only setting move, but it requires the most specific situation.