So Vainglory is quite good on the iPhone 6 Plus, looks amazing as well.
i think the ui of vainglory works much better than fates forever, in fates my hand kept obscuring the ability buttons (i'm left handed) making it hard to hit them in a hurry.
plus the weird unintuitive system for the abilities in fates makes it harder than it should be to do things in the heat of the moment. like some of them where you drag a line for it to follow make sense, but when you have to drag a cursor from your character onto an enemy to target them it just overcomplicates things for no reason. the way it denotes that is super unintuitive as well so it takes a lot of time to get used to what motion you need to make for which ability.
vainglory looks amazing and the map layout seems clever and does some new things compared to other mobas. my only concern is the character variety is part of why I enjoy LoL and all the tablet mobas have a fairly small number of characters