I was hesitant to go from iPhone 5 to 6+ but I really wanted the 1080p screen for movies and other video and OIS for the camera. I liked the idea of a bigger screen and had held a few large Android phones for a few moments to test the waters. The cellular store has 30 day trade-ins if you don't like a new phone so I figured I'd get the 64GB 6+ and if I didn't like it, trade to a 128GB 6.
The 6+ has worked out well for me. it fits well in my hands. I rarely have to use Reachability, but the feature does come in handy. I occasionally get myself in an unconfortable position where my hand cramps. This is usually because I'm trying to multitask with the physical world.
When I view a 6 or 6S screen, I notice the resolution difference and I don't like it. I really enjoy watching video on my phone and have a case with a stand just for video. I use my phone in my car and with it on my dash it makes a nice car radio.
It'll be 2 years with my phone this fall. If I don't break it, I'll be holding off for the Anniversary iPhone and will be getting the Plus version; depending on what the lineup includes.
If I decide to go to an Android phone, I would probably get a similarly sized screen.