Othello and King Lear are two plays about how mistakes in judgment brings the lead character's downfall, but Othello is really brought down by Iago, who understands his blind spots, including Othello's own personal weakness, sense of outsiderness and jealousy and King Lear is brought down by his own hubris, telling his daughters he'll grant the largest share of his kingdom to the one who loves him the most (in other words, he basically begs them to tell him they adore him and flatter him as much as they can; it is hard to love that king) and then depriving his youngest daughter of her share when she refuses to do his bidding because she says words can't express her love for him.
Lear, impressed with his older daughters, decides to split his kingdom evenly between the two of them and live alternatively with both and their husbands. But the two older daughters, while talking to each other, show their declarations of love were fake. They view the King as a fool and are only interested in his wealth. The play is full of their machinations and King Lear becomes completely mad. As in Hamlet, in the end just about everyone dies too.
These plays are two examples of how envious people can worm their way close to a decision maker and set him against someone he believes in for their own personal advantage, either revenge (Iago is angry that Othello promoted Cassio over him) or greed (King Lear's older daughters want all of his kingdom). I saw Otello at the Metropolitan Opera - the opera version by Verdi, obviously not the Shakespeare play, hence the slightly different title - in a stunning production by Bartlett Sher, while the Shakespeare's Globe production of King Lear at ArtsEmerson last year was underwhelming at best.
Hence, I find myself more interested in Othello because it made more of an impression on me, but I think there is more value in studying King Lear. You can protect yourself from someone like Iago by knowing your blind spots, and understanding that people who talk to you about other close associates may not have your best interest at heart.
My opinion is that it is best when dealing with Iago types to pretend to believe them while you watch your back, so that they don't change their plot to trying to get others to destroy you, and to firmly and definitely cut the Iago-type person out of your life as soon as you can.
(Othello in particular should have known Iago would not be happy about being passed over for promotion, and lo and behold! suddenly Othello starts seeing ties between Cassio and Othello's wife. Come on, Othello, how can you fall for that? More interestingly, perhaps Iago was never a viable candidate for promotion, so that he is a legend in his own mind but a mediocre soldier on the battlefield - perhaps Othello has no clue he feels wronged because he was in fact never in the running.)
But King Lear offers valuable lessons for aging people at the top who, in their eagerness to prove to themselves they are loved, may not only end up looking like fools but also watch as what they loved is destroyed.