Presuming that "reasonableness" means a "reasonable chance of setting the contract, the matter is better viewed by asking what holding do we need opp/pd to hold for our lead to take four tricks? The optimum lead is a lead that will set against all of the holdings that will allow for the contract to be defeated. We can reasonably give pd no more than 2 hts and either the A or QJ of clubs. With our reasonable diamonds, opps are not likely to be able to pitch all their hts before Pd or I get in. (And if they can, it might not matter what we lead). King of Clubs works whenever pd holds the Club Ace and one ht. Pd can overtake or not, depending on dummy number of clubs and rtn a heart for a ruff. If holding two hts, rtn a heart for the setting trick. It also works if pd holds Club Q, figuring you will get in with your Diamond K or Trump Ace before opps can pitch losing club. If works if RHO holds Heart King. The Heart Ace looks good but it only works against a few select holdings, many of which are also going down with the lead of the Club King. I have no problem playing Ace of Hearts and out a heart knowing Pd is short in hearts and I hold the Trump Ace. However, what reasonable holding in hearts are you giving the opps? If RHO is short hearts, a ruff that is overruffed does no good. and if hearts are 5/4/2/2, one bad club might be going on a heart if trump are 2/1/6/4. As someone else well stated, the opps have distribution.