Both the phones are good as Redmi note 3 has a better processor in terms of performance.. but Redmi note 4 processor has a better processor in terms of power efficiency. as well as it has more RAM as well
Both Redmi Note 4 and Redmi Note 3 are very similar on the sepcification front, But Xiaomis focus with the Redmi Note 4 is on offering a better design, more storage space, RAM options and a more power efficient processor.
Redmi Note 3 is better than Redmi 3s. It offers better specs and performance is also good. But, it's price is slightly higher than Redmi 3s's price. If you are okay with the price go for Redmi Note 3. Redmi Note 3