After using lots of different models I bought a pure Android Nexus 4, it made such a positive impression on me that I was very eager to buy a Nexus 5 upon release due to it's better specs.
Now after one year with the N5, I'm super happy. I've had other new phones as you can see by the list on the left of my current models. But if i was going to limit myself to just one it'd be a Nexus hands down no hesitation.
I'll be ordering a Nexus 6 tomorrow because I have a distinct need for a large 6"display. Yet I'm also keeping my Nexus 5, its like new even though it's had lots of use. It's just too good to sell.