IPhone 7 plus is apple's latest flagship device. It is smooth, fast, optimised. iphones are well know for their hardware software integration. So this one is not an exception. iOS optimisation is best. You will not feel any lag or whatsoever. It is water resistant, have dual camera which has an amazing portrait mode but it lacks some basic features like fast charging, a 720p display. It is priced higher as compared to other countries.
If you love iOS go for it but if you can live with android go for s8, which is a very beautiful smartphone.
