といい～といい

といい～といい names two sides of one thing and then passes judgment on the whole: "both in X and in Y", "whether you look at X or Y". Each といい goes straight after a noun, and the evaluation comes after the comma.

The two nouns are samples. They stand for everything else you could have mentioned, so the judgment after them is a strong one, for praise or for criticism. The second half is an evaluation, not a plan or a request: ×デザインといい機能といい、このスマホを買おう.

も～も or といい～といい

も〜～も lists two things and says the same about each. といい～といい picks two aspects of one subject as evidence for a verdict on that subject.

The pattern sounds a little formal and turns up most in writing, reviews and speeches. Casual talk more often makes the same point with ～し～し.