I would like to echo napalm's senitments.
After doing a lot of research into the matter, I genuinely am baffled as to why EVERYONE doesn't buy the Nexus product line. I'm convinced that it is due to the almost zero marketing that Google does for its Nexus line. (just as a caveat, there are several niche purposes for which other phones do make sense, such as having a stylus, or a removable battery, etc.)
The biggest appeal of the Nexus product line for me is the price. You're getting premium specs, which on comparable phones costs $700-800, for only $350 (again a few caveats with that. But for 99.999% of users, those caveats aren't relevant).
And I've definitely put my money where my mouth is: over the past 2 years, I've bought 2 Nexus 4s, 5 Nexus 5s (a phenomenal phone, I still prefer it over all 2014 launches), and 2 Nexus 7 (2013 version, these are 7" tablets), for various family members.
I would strongly urge anyone considering a smartphone to go for the Nexus line. Their new tablet and phone are going to be announced in a few weeks (I think Oct 16 for the tablet); I'm definitely keeping an eye out for that.
2 asides
1.) If you want a low cost premium phone, there is a "new" manufacturer, OnePlus, which offers high-end specs for a marginal price. However their supply is very limited and I haven't been able to buy one to comment on it. But just for full-disclosure, on paper at least, the OnePlus One looks like a darn good phone.
2.) If you still wish to have the latest version of Android (btw, with every new version of android, Google launches a new Nexus phone. We should be getting Android L in a few weeks along with the new Nexus announcement), but still want a Samsung or whatever, you can buy a Google Play Edition (GPE) phone. For some of the most popular flagships (Galaxy S line, HTC's M line, etc), Google does offer a GPE phone and will update it itself very quickly as opposed to waititng for the manufacturer to update it.
However unlike Nexus devices, GPE phones still charge you a premium rate (so $700 or so)