This question cannot be answered neutrally and abstractly. To answer this we must objectively evaluate the smartphone as a device and subjectively evaluate it to my daily life requirements.
I love to find a guiding principle in a matter. This is how I can remain with a Android and a IPhone at the same time. Android has some phenomenal forum apps and IPhone is now fast and crisp as a experience.
I find the email experience and social networking and camera now awesome on IPhone 6s. But my galaxy s6 is awesome for camera; forums; Instagram; and performance.
Do I need 2 devices? That is a subjective question that has an illogical answer. Yes. However I like the IPhone 6s and I have had 2 updates in 3 days ; I cannot retire the s6.
Does everyone need 2 devices? That deserves a objective answer. No. It is a luxury which few can afford.
More to come!