Which Android phone should I choose?

Hi all!
I'm actually an iPhone 4S user and this summer (in June) is my birthday and, as a present to myself, I'd like to change my phone.
I've never had an Android phone (yes, my girlfriend has a Nexus 4 because I told her to buy it and she's very happy with it), but I can't decide which one to choose.
The three that I'm looking for are the HTC One, the Nexus 4 and the Samsung Galaxy S4.
I like also the new Samsung Galaxy S4 "Nexus Edition", but I'm Italian and, so, it won't ship to my country.

Which one, in your opinion, an iPhone user should pick?

Thank you!