Replying to Tough Decision

Alright, here's the deal.
I am about to switch to the mobile service provider Sprint because fuck Verizon.
I currently have a Samsung Note 4, but have a MacBook Pro which does not connect to my Samsung cause of Apple's dumbass closed interface.
I have to turn in my current phone to Sprint to get my new one, so I could possibly get an iPhone 6+ or just get another Note 4.

All I really use my phone for right now is to take pictures, look up addresses for my job, and texting/calling, snapchat and music(Spotify and the default music app). The only time I really ever used the S Pen was when my touch screen got fucked up and only the S Pen sensor worked, so it wouldn't be a big deal if I didn't have it anymore. I rarely use the multi tab screen function.

I'd like the iPhone because of the better picture quality, and the ability to actually be able to connect my phone to my computer and work with it through there.
-I'm not totally sure how iMessage works so could someone explain that? Can you still use it without WiFi?
So if someone is another country, and sends me a message through iMessage, would I be able to view it without having WiFi.
My data through Sprint would be unlimited, so I wouldn't have to worry about that at all. Especially since I only get 2GB of data through Verizon which is some bull shit considering how much data snapchat and maps use up.

I don't give a fuck that the iPhone 6+ bends sometimes.