Personally I wouldn't touch a BlackBerry anymore, they're ok as a work tool but having to support them as part of my job I wouldn't pay my own money for one.
I have an iPhone 5 which I really like, it's fast, light and is really nice to use. From my experience the main competitor is the Samsung Galaxy SIII which is also a great bit of kit. Also if the Nexus 4 is anything like the Nexus 7 tablet it'll be a cracking phone too.