Which phone to buy?

I'm torn between buying 3 phones when I move to Japan, currently I'm a Samsung user, but I've hardly seen anyone use the galaxy in Tokyo, and my wife pointed out that there aren't really any Samsung stores in Tokyo, where there are a lot of Apple stores, so if I had a phone issue, it could be more difficult with Sansung.
Either way, I'm going to buy SIM free in America, but what I'm torn between is the Galaxy 7 (maybe the edge, Note is too big for my taste), iPhone 6s or the iPhone 7s.
I'm also going to get more into App development in Japan, so I feel like iPhone may be the way to go because of Swift...but I've only had an iPhone once before, the iPhone 4s and it was a work phone, not a huge fan, I always liked the freedom of a Samsung, but in Japan I have my doubts...

There are no Samsung stores in Tokyo. The brand new Samsung phones are available at Docomo and au shops.
And also, there are second hand Samsung phones are available at shops such as Sofmap and Boofoff stores for both Docomo and au sim lock phones, which you can make a contract with only Docomo or au.
I'm not sure you can buy a Sim free Samsung phones in JP which I have never seen in stores.
If you have a sim free Samsung phones which you have bought in US, I think it will work in Docomo line MVNO, but not work on au lines. au uses slightly different band lines.

Thank you.
Judging from what you said, it is as I expected though, iPhone would be less of a headache.