Iphone Series: Recommended model (Iphone 6/s)
Great user IO, really simple, gets the job done, plenty of apps. Go to phone you cant go wrong with
Android Series: Recommended model (Samsung Galaxy S7)
Solid, runs fast, high customization, and plenty of apps to use. Recommended for the more advance teched people
Windows Phone: Recommended Model (Lumia 950XL)
IO is the same across all devices, Camera is of the best, passing even normal cameras, "No device left behind" meaning newer versions wont bog down your older phone, average amount of apps and survivability of the phone is great. Recommended for those who take plenty of pictures
The phones I used to own (In order)
iPhone 4
Lumia 920
Samsung Galaxy S7 Edge
This is of past experiences and knowledge, You might have noticed I wrote a little less for the Android, thats because I owned the iPhone and Windows phone for about 3 years and just 2 months ago I got the Android so thats all the strong suites I know.