Answer
You (dealer, both vulnerable) are on lead against four diamonds doubled, after a contentious auction.
What’s your lead? It’s reasonable to hope that your J943 of trumps will provide a natural trump trick, perhaps two. For that reason, we wouldn’t have any interest in arranging club ruffs. Indeed, it sounds as if declarer has long strong clubs, so a club lead may well damage partner’s club holding. Clearly it’s dangerous to lead a trump. Leading away from a King is dangerous at any time, so we would rule out a heart lead. We would lead a spade by process of elimination.
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