It's really so apples and oranges (no pun intended). They both have their strengths, they both have their weaknesses....and at the end of the day, they're both killer products.
I have an iPhone - a 6+. I do not have a Samsung, though I used to - a Galaxy Note 3. I have no plans to buy another Samsung, never say never, I guess, but nothing's on the horizon. I WOULD like to have an Android phone as well as my iPhone, though, and alternate back and forth - same with a Windows phone. But if I ever do get to get back on the Android mothership, it's gonna be via a Nexus, and not a Samsung.
But even with all that said, I STILL can't say that the iPhone is better than the Samsung.......It's just too darn give and take!!!
In terms of the raw hardware, I do think the Samsung is easily the better (the screen has no equal in the market, and the camera is arguably the best as well), plus the design of the thing, IMO, is a little bit splashier than the Apple. But in terms of software, I think I'd have to give the crown to Apple. It runs cleaner, leaner, safer and all of that. Plus, if you have or plan to have any other Apple products, you always have Handoff, which to RADICALLY oversimplify, sort of syncs all your Apple devices. Very handy, and you'll be out of luck on that front with the Sammy.
When it comes to Apps, between the two, Android has more apps....but Apple arguably has better apps. They tend to get updated first, and be more polished. Plus, while the Apple App Store may be a little bit draconian in its stringency, the Google Play Store, by comparison, is the Wild Wild West, and not only are you gonna find a ton more garbageware apps, or apps that are real clunky, but you can also even find things that will actually hurt you, though they certainly are working to shore that up.
However, in terms of the [quote unquote] "essential apps", they're both gonna do just fine for you.
But I think the big thing you have to decide is which operating system you like better. Do you like the look, the feel, and the feature-set of iOS better, or Android? Android is a LOT freer, and more flexible, and more customizable - you can "make it your own". But Apple is much cleaner, and safer. Android also has an app drawer, so you don't have to keep all your app icons on your main screen(s), which is handy, and Android also supports widgets, though with Apple, you can have an unlimited number of apps in a folder, which does help to offset the lack of app trays somewhat.
Apple doesn't support widgets, but widgets can be a big battery drain too. And even with the addition of "doze" to Android Marshmallow, the Android phones are still gonna chew through their batteries quite a bit faster.
A Nexus (if you want a third option) runs a much more "pure" Android experience than a Samsung (which modify the Android on their phones with a new user interface, and a suite of apps and features collectively referred to as "Touchwiz"). Some people love the look and feel of Touchwiz, and get serious benefit from the added features and functions. So I'm not here to bash Touchwiz....but I personally want no part of it. I MUCH prefer the look and feel of "vanilla", and don't really benefit from the extra features. Also, while "vanilla" Android is still quite a bit less lean and clean than iOS, and while "vanilla" phones still don't get their OS updates nearly as quickly as iOS, they are still much leaner and cleaner than Touchwiz devices, and can run as good or better on inferior hardware than a Touchwiz phone can on superior hardware (see Nexus 6p vs Galaxy Note 5). Plus, Nexus devices running "vanilla" get updates MUUUUCH quicker than Sammy devices do.
I liked the hardware on my Note 3, quite a lot, heck, in some ways even better than this 6+! But it's the software, the battery plummet, and the eternal waits for updates that will keep me from coming back to a Sammy! Now, this kind of stuff may or may not matter to you. But if it does, and you decide to go Android over iOS, then I'd SERIOUSLY consider it!
Anyway, the good news is this: you really can't go too wrong either way (an iPhone, a Galaxy....or a Nexus) The bad news: whichever one you get, you're going to miss out on the other ones, and they are awesome things you're going to be missing out on. So don't be too surprised if you don't feel a tinge of regret when you see one of the other ones in the wild. That's just what happens when you have to pick just one awesome thing from a pool of awesome things. I was in an elevator with a guy who had a super shiny new Samsung the other day, and I felt it, even with my commitment to avoid Samsung.
As for me, and what I prefer, I prefer both...but differently. The distinctions I like to use (I'll use two that basically accomplish making the same point) are a) "left brain" (logic, reason, practicality, "adulthood") vs "right brain" (passion, emotion, taste, urges), or if you prefer, b) "head" (same in this case as "left brain"), vs "heart" (same in this case as "right brain"). My left brain (my head) prefers Apple, and my right brain (my heart) prefers Android....I'm using an Apple, though.
Wishing you all the best!!! Let us know what you choose! I think you're ultimately going to be okay either way.
If you do go Samsung, go ahead and spring for the brand new S7, rather than last year's S6. Then again, iPhone 7 is not too far away, so do you really want to spring for the 6s so close to new phone time? Also, the Nexus 5x is fairly ho-hum. I'd probably skip it. The Nexus 6p is awesome, though...but at 5.7", it's quite a bit bigger than the 6s and S6 you're looking at, so if that's too big for you, then maybe just skip Nexus this round.
Cheers!