On this auction it is unlikely that the opponents are wide open for a big set. Nevertheless, partner's conventional double means he believes he has a chance to set the contract if you lead through dummy's first-bid suit. Additionally, he may be trying to warn against your "normal" lead as being least likely to succeed and most likely to cost both time and a trick. The diamond is most probably the lead he is warning against. Hence a club lead gets a higher award than a diamond. However, if you insist on opening a diamond, the queen offers a better chance than a low one.
If your side can win a trick in the heart suit, you want partner to win it, and you also want to tell him to return a club. He knows you have more than a four-card heart suit, so your lowest card must be a suit-preference signal. Chances are against winning a heart trick, however, so the diamond lead may be an attack in the right direction.
After partner's cue-bid in clubs, showing the ace or a void, the only question really is which club should you lead. The 10 gets top award because it confirms that your strength is in the higher of the other side suits and that partner can afford to underlead the ace of hearts to put you back on lead. The 5 of clubs hints at the same message, but the 3 or deuce would strongly suggest to partner that you have a quick reentry in diamonds and therefore scores even lower than the stodgy lead of the king of hearts.