I want to clarify about the processors?

Question

Iron

I want to take a laptop. Decide for yourself to take with an intel core i5 processor. My question is which processor is better? there are intel core i5 3xxx (3 series) and 4xxx (4 series). I thought that the processors of the 3 series are already the old generation and the 4 series of the new generation. But I read a comment from a laptop representative, he says that the 3 series is more productive than the 4 series, in general I'm confused, can you advise which one to take better?