Hi Marie,
Thanks for the compliment above! This is a question we hear a lot and argue (lovingly) amongst ourselves on the AC team. Currently, I use both Android and iOS heavily on a day-to-day basis. There are HUGE advantages to both platforms, and i'm going to try and provide an unbiased few since I have such respect for both. Some of points will be specific to the GS8 vs the iPhone 7. Be warned though, this question will open up a can of worms on the site

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Why stay Android?
-Customization- making your phone look how you want, moving icons where you want, getting everything in place just how you like it.
-You experience with your current Galaxy will take you far. Not having to relearn a new device is a huge advantage and a frustration saver.
-The best phone display ever created (specifically the Galaxy S8 I realize this is more specific than Android in general)
-Most android devices including the GS8/+ have the ability to expand storage on the fly- this is something iOS users don't get to experience. Great for movies, music, pictures, apps, etc...
-Unique designs. Androids come in all shapes, colors, sizes, and stand out from the crowd!
-Camera on the S8 is best in class right now. If you love taking pictures this is a nice incentive. The i7 is no slouch, but the camera comparison tests are in, and the GS8 is winning.
-The ability to quick charge your phone. Juice up if you are running low on battery very quickly! Huge advantage when you only have a few minutes and are running out the door.
Why iOS?
-As you mentioned above. EVERYONE USES IT. Theres a reason its one of the most popular devices in the world. Little things like being at someones house and being low on battery. Chances are they have an extra iPhone charger you can borrow- not likely a USB type-c cable

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-It works day in and day out exactly how you intended it. This is the one thing that sticks out for me always. I never need to reboot the device or tweak it.
-iMessage is a great text message communicator. Having iMessage with the immediate family is a plus for sure. There are little personal touches this text messaging platform brings over just standard SMS.
-Facetime is the perfect video communicator for families. Yes, there are other platforms out there like Duo, Skype, Hangouts that do video calling, but as we've discussed the vast majority of family members have iPhones and they are one click away from video chatting without having to download apps and add usernames. This is huge if the family isn't geographically close, or just talks a ton!
-Updates the day Apple releases them no matter what carrier you are on. This bugs me about Android and the carrier control over updates. I bought a Pixel for this very reason. I love that Apple gives you the latest software and everyone gets it the same day.
-Longevity- I think Apple devices get a little more life out of them. The software continues to perform a little better over time.
-Usually first to get app updates over their Android counterpart apps (not always but most often).
I absolutely love both platforms, and its why I use both on a daily basis! Always remember the 14 day return policy via your carrier. If you aren't satisfied with the 1 option exchange it for the other!