I have both a Galaxy S7 and an iPhone 6 (don't ask). They're both great... the iPhone 6S has even newer features than my 6, like a better camera and that 3-D touch thing, that hasn't exactly set the world on fire. I agree with the suggestion above to take a couple of phone shops: someone paying you even a pittance for something you would do anyway, or that has value to you is a good use of your time.
Since I use both platforms every day, here are my impressions for each:
iPhone:
-Super easy to use. If you're at all worried about the learning curve of a smart phone, this might be the one for you
-The 6S actually has a higher resolution camera than the Samsung. There's some indication that the Samsung's camera is set up in such a way that it gathers more light and takes better photos, but my iPhone 6 has a inferior camera than my Samsung. The camera on the 6S is supposed to be better than both.
Samsung:
-It's literally the newest phone out there: it was just released a few weeks ago, so it will be the longest until it's old news. That means it should be supported for the longest if you're like me and don't buy new phones often.
-It's water resistant.
-It has an external memory slot, so you can use external memory cards if you use a lot of space on your phone (or you just never want to delete MS photos, ever).
-It has more flexibility and settings, like the ability to switch to "super duper power saving mode". There are lots of options like that, which make it more flexible, but also more complicated than the iPhone.
These are both the highest tier phones, which means they're super expensive. If you're interested in a lower cost smart phone, there are probably some good ones. This, I think, would be a situation where doing some cell phone shops would be great. You can ask the rep about whatever phone they want info about, and then ask about any lower cost options and you can compare how you like each phone against each other.
Shopper in California's Bay Area