Nexus 5, very well built handset. Slim, big screen. £299 for 16gb compared to £550 for iPhone.
But few people want big screens, as they are too cumbersome. I agree with many, the iPhone 5 is too bloody big!
I used Nexus 5 for two weeks, it nice and slim, very lightweight, went back to my iPhone 4S. The screen feels so, so tiny now. Hoping to blag one for work soon, the iPhone 5 size does not work for me.
The screen on the Nexus 5 is simply awesome, the 3d pano's blow iPhone basic ones out of the water. I've been iPhone fan for a while but latest gens have been woeful, got 5c in office. No one has "borrowed" it as it offers no improvements.
I managed to convert an iOS scrum master to the Nexus! 
Nexus 5 is too big. Simple.
I can see nothing wrong with the 3GS screen. It does the job. Shame the phone is too slow now, and lacks 900Mhz 3G capability, else I'd go back to it tomorrow.
There are 2 reasons why I won't go to an Android based device yet, which I've said before:
1) Email/Collaboration is very important to how I organise my life, and nobody does a useful, secure Android email client yet.
2) Google do not create and maintain a mobile OS for nothing. Their nature is to be aggressive and intrusive. They make crApple and MS look like angels.