My favourite was the Nexus 4, the only issue I had was crappy battery life due to the battery being such a small capacity. Its a shame really as I like the customisation etc with Android, I mean iPhone is just boring really.
Battery life on my nexus 5 wasn't great either. As far as Android goes it was easily the best, cleanest, leanest, most functional of all the Android phones I've owned. The phone could take a beating it never even got warm and was fast, no glitches it just did it. Was on par with iPhone as far as worry free performance.
Screen was beautiful and one of the best touch screens sensors out there, so responsive.
The reason I ditched it for iPhone because the nexus 5 speaker is terrible, worst I've ever heard on aby smartphone, even turned all the way up could barely hear the thing.
The camera wasn't bad in video and picture quality , but nothing special as it over time started to have auto focus issues where I always had to manually struggle to keep it in focus while recording video.
If the speaker and camera were better I'd have to say it would of been one of the best phones I've ever used. I don't like Android, but LG did a good job on it.
IOS can be boring and I about threw my iPhone 6 at the wall when I first got it... Took me a few days to fully figure it out not being familar with it and so familiar with Android... When I did figured the iPhone out I liked it much better than Android...