Play the one you'll be known to hold ... continued.
Ready for the full deal? Let us analyze our chances, without looking at the
other 26 cards, given South's 3 Aces we see every honor. South opened a
paper-thin 1 NT, this is a "bad" slam, but dummy is disgustingly good.
If
declarer has 4 diamonds, it is "cold". If he has 3 clubs he is always
down, but what if he has only two, as in the diagram (or only 2 diamonds, which
leads to the same position)? Can you see how he
will make, how dead a duck you will be?
Declarer has but one option, he knows where the Jack of Hearts is, never mind your clever Queen. The play will proceed: Spade Ace, catching your Jack, Ace of Clubs, King of Clubs, club ruff, 3 rounds of diamonds, followed by a trump to your King: an endplay (give a ruff-and-sluff or lead into the A,10 of Hearts) ending your chances.
That is why you had to think while declarer was thinking. When he leads his Ace of Spades, at trick two, drop the King, in tempo. Now he sees the contract safe, by "picking off" partner's Jack and will not even think about stripping out the minors ... that risks a ruff. He will finesse, you win the Jack, return a minor and enjoy your Jack of Hearts in the fullness of time.
Observe, that there is absolutely no danger in playing the King of trumps under the Ace at trick two. Whatever his distribution, declarer will never have reason to forgo the finesse for the Jack ... unless he is incompetent. But, remember the introduction: these people are better players, than your foursome.