There's been tons of issues with the Samsung S6 and S6 edge due to antenna placement. Do your research and find the phone which best meets your needs.
I appreciate the interconnectedness of the iPhone with my other Apple hardware, software and other iPhone users. If you use iTunes for your music, and other Apple software and hardware, or appreciate the level of security offered by the Apple ecosystem, this phone may be for you.
My brother uses a Windows phone for a parallel reason - it interfaces well with the purely windows world in which he operates. IF you are using Windows 8.1 or 10, with One Drive, Outlook and Office 365, this would be a good choice.
Android phones, work especially well if you have migrated your computing experience to the Google suite of productivity applications. If you use Gmail, Google Drive, Google Play for music, Google photos, etc., then one of these phones may be for you.
If you don't fit any of the above categories, then any of the phone might meet your needs. I feel Apple stands behind their product better than any of the other companies, but YMMV.
If you're asking about which iPhone to get, I'd choose the newest, as it will be useful to you the longest.