I recently switched from iPhone 5 to the Galaxy S6 Edge and I love my new phone. Especially after the Marshmallow Update. This is what I have learned since switching.
iPhone = Optimization, Android = Customization.
The iPhone locks you into certain features and setting, which helps provide security and can make things run smoother. Whenever I tried using a feature it either worked or didn't work.
The Android allows you to have a lot of control over your features and settings. You have to put in a lot of effort to make the phone work exactly how you want it. For the most part I can use almost any feature I want but sometimes I have to put in a lot of effort to get it to work and I don't always have the motivation to do that.
Both phone are good phones. It just depends one what you are looking for in a phone; something that works well with little effort from the user, or something that gives you free range over a lot of features but can require a lot of work.
All iPhones get software updates at the same time. For some android phones, you have to wait for updates for a long time.
For my phone specifically, it took me a while to get used to, but I finally have my phone set up the way I want it to be. The camera on the S6 is amazing. Seriously, look up Galaxy S6 photography. The battery life is not the best, some users have great battery life and some users have terrible battery life. You can download apps or root your phone that can help save your battery life by disabling software. I watch netlfix on my phone while at work, so I usually have to charge it around 1 or 2pm. I love the edge screen. It creates quick shortcuts to apps and contacts, but it's not really necessary. The regular S6 is just as good.
I love Samsung Pay. I only downloaded it so that I could get a free wireless charging pad (which I would never spend money on but I use all of the time), but it's fantastic. It works at almost any place you swipe your card. Apple Pay and Android Pay only work at certain places that have card swippers (I can't think of what these are called) modified to accept these. But Samsung Pay works with most card swippers. They somehow got it to work with the old electronics instead of having to install new card swippers. Sorry if I am not making sense.
TL;DR Apple phones are designed around optimization, while Android phones are designed around customization. If you want something that works well right out the box, go Apple. If you want something that can be customized to better fit your needs, go Android.