I would recommend going with a Nexus 6.I have one and its absolutely amazing.SInce you're switching from an iphone,you must be used to a lag free environment. Thats exactly what the Nexus offers.As for Sprint,it should work(do some research) as it has some really good radios.The reason I recommend this is also because of the screen size you're mostly used to.The iphone 6 plus and the Nexus 6 are roughly the same in physical dimensions except that the Nexus is a bit thick but thats due to the curved back.Much better display and .5 inches bigger too.If you're more into newer hardware and more customizeability then the Moto X Style is what you should get.But since it was newly released I seriously doubt it will be easily available.The Nexus 6 prices have also dropped significantly since a new Nexus 6 might be released soon.As for the Style working on Sprint,like I said before,Motorola usually has one of the best radios though you should still do some research.Hope this helps.