One would be the Apple ecosystem. Another would be how the devices work great together and complement each other. Perhaps the best one would be the guaranteed OS upgrades. At this point, however, a better comparison would be against the iPhone 6s.
To me the iPhone has better (more readable) notifications at the lock screen. On my S4, I pretty much have to open the message or email to get much out of it. If I had two or more emails waiting, I was only told I had two emails, and zero content about either one of them. Very annoying in my IT role when I get maybe a hundred emails a day, and serve a large building (out of my office a lot). But I retired last month, so it doesn't matter anymore.
I've had two Samsung phones before and they both had massive bloatware that started giving me headaches the longer I had it. If you decide to stay with Android, I would recommend looking at another brand.
As mentioned in post three. The top advantage is the ecosystem. The iPhone will work pretty seamless with your MacBook Pros. The OS gets updated at a pretty frequent rate. Straight forward and simple to use.
I would also suggest with it being so close to September/October (if you end up deciding on jumping to the iPhone) to hold out for the new 6s or 6s+. It will have double the ram of the current 6/6+, also rumoured to have a jump from 8 to 12mp camera (possible 4k video recording) and a brand new feature of ForceTouch (same tech used in Apple Watch and new trackpads in the retina MacBook and 2015 MacBook pros.)