Feature wise, iOS8 basically caught up to WP8.1. It's still behind KitKat.
As a comprehensive OS though, it's probably around the same as Android, and just behind 8.1.
To be honest in terms of out of the box phones, pure android and IOS 8 doesn't much in it, some things iOS has, pure android doesn't ( integrated out of the box face time, some of the new i message features, continuity, a proper personal assistant )
in face I have the nexus 5 and it's pretty bare in terms of features if I'm honest, One could say it's as "boring" as Ios. What sets android apart is the customisability which iOS will probably never have.
its also hard to compare iOS with android, because there are many different versions of android , so some phones have features that are not on pure android.
I have had the note 3 with touch whizz and the operating system running android is just a piece of bloat ware if I'm honest, I hated it and considering the hard ware at the time was meant to be the best, it's actual real life performance just wasn't up to scratch.
then I got the nexus 5 and it's every bit as smooth and silky and beautiful as iOS IMO.
however like many people who agree, it seems iOS has caught up with Android in terms of main Features, Surpassed in in some areas, and looks more beautiful than most forms of android ( Since there are many forms of android).
I think Ios8 is a massive step in the right direction, I would love them to include more customisability one day, Maybe realising a good API to change the look of the operating system slightly , without inflckting on performance.
But either way android will live on, and so will iOS.
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I think the real question is, will android performance ever be on par with iOS. You can put in a bajillion gimmicky features into a device. If it's not convenient to use or doesn't run smoothly. What's the point?
Pure android is already as smooth as iOS IMO, my girlfriend has a iPhone 5s, and in some cases it seems my nexus 5 is snappier , it's also buttery smooth.
The problem is people compare the performance of touch whizz etc when in reality all that says is samsung can't development software for sh**.
But pure android for me is beautiful , runs smoothly and like iOS, doesn't contain an actual lot of features.