My main issue - and this was true for the last Android phone I had as well - is that the device just turns into a slow, glitchy, shit-battery, near-unusable brick after about a year's time. All the while I see my parents and others' iPhones chugging along just fine after two years. Have Android phones gotten better in this regard? Have I just been unlucky?
No, not bad luck. Unfortunately, that's one of the compatibility issues that surface when horrible "skins" like Sammy's TouchWiz are placed on top of Android. And they really are completely different OSs in practise.
So you update all of your apps and the device progressively becomes slower and clunkier. Pretty normal, especially for a GS3.
iPhones managed to get durability better, but iPhone 4s today are laggy and slow in general (or at least mine is) and even 4Ss are not as smooth as 5s and 5Ss - not by any means unusable though.
Anyways, we've now come to a point where components are plenty powerful enough, so that even a late 2013 phone will probably be holding up well in 2015, especially a device like the (stock) Nexus 5.
As of now, I'd say that the yesterday-revealed Moto X is the one with the right to claim Android's throne both for hardware and software (although it still has to be proved), while the Nexus 6 (coming this Halloween, approximately) will 99% be a safer bet, despite probably being a little more of a tool rather than a 'personal' and sexy-looking design object like the X.
Bear in mind that these are just assumptions
I am making though, for I have been into the tech "business" for a while now; but that also tells me that I could be completely wrong, especially given the fact that Motorola themselves seem to be in charge of the next Nexus.
If you really, really had to buy a phone this moment, I would like to recommend the OnePlus One (which is the phone I am currently using), but to get one isn't exactly the easiest thing unfortunately, so it would come down to either the semi-jump-in-the-dark Moto X or a GPE HTC One for me. But again, that depends on the user's demands.
Holding on a couple more months is still the best possible thing to do in my opinion, since a lot is about to change in the Android space thanks to L and Material Design. And by the holiday it'll be a triple-threat between the new Nexus (or Nexii, possibly), the Moto X and the OnePlus One, which should be publicly available for purchase by October.
Never going to recommend a 'skinned' Android again.