In Othello, what sort of person does Iago criticize and what kind of men does he admire?
Iago's interest, in the play, is in the specific people he interacts with and whether he has had preferential treatment or not. And, overall, his interest is in himself. As I describe below, he does have at least one moment where he seems to discuss the sort of man he admires, but it really boils down to admiration of himself.
He criticizes both Othello and Cassio in Act I, scene i, but it is easy to see that it isn't because of the sort of people they are. It is true that he speaks of Othello as "The Moor," lumping him into a racial group rather than speaking of him by his individual given name, and he slights Cassio's experience in talking about his promotion by Othello, but he says very clearly that his interest in all in his self, so these comments must be viewed as only relating to the personal slight Iago feels in regards to these characters, rather than being a general comment about the types of persons Othello and Cassio are.
In Act I, scene i, in his speech beginning at line 41, he does mention that "honest" men who follow their masters (or leaders) simply because that is the protocol, are, basically, chumps. He says that every man should look out for himself, regardless of who he has pledged to follow. He says:
Whip me such honest knaves: others there are,
Who. . .
Keep yet their hearts attending on themselves,
And throwing but shows of service on their lords,
Do well thrive by 'em, and when they have lin'd their coats,
Do themselves homage. . .
And such a one do I profess myself
And so, even though Iago has allied himself with some other types of men he could be said to admire, it is really himself that he admires and himself that he looks out for.
For more on Iago and Act I, scene i, please follow the links below.