I'd say iPhone 7 but we don't know what it looks like 100% for sure or its specs etc. I have a 6S plus and my friend has a 6 plus. Not much difference really and we both love our phones and won't be upgrading any time soon even with the 7 coming out in September. Also apple always pushes out iOS updates and supports even their old phones while other phone makers don't.
As far as one plus 3 goes if you trying to save money and etc then go with it because it will not be too pricey and one plus 3 will be for sale without an invite.
Galaxy note 6 will prob be like similar to s7 etc, finger print magnet as usual and be full of touchwiz crap etc. Only thing note 6 will have going for it that the s7 already has for example will be their killer cameras and etc. If I could use iOS legit etc and not jailbroken I would get a galaxy s7 or a galaxy note 6 such as you are thinking about.
Get the iPhone 7