IMO, there's no question that you should wait for Google IO. If a new phone isn't announced then, it's probably not going to be announced until the fall/December.

Unfortunately the leaks have been very few about a new phone. Early on it was the rumors of the Motorola X phone, which I thought was the last of the pre-acquisition pipeline (which even Google reps were calling crappy). Then there were rumors of a good Motorola phone, but still not a "Nexus" device. Then the last I heard was that LG would again make the next Nexus phone, but who knows?

I have a Galaxy Nexus, and I've had it since release day. For a while there, I'd rooted it and installed the AOKP ROM, which I regret due to the immense aggravation it caused due to HORRIBLE performance issues. It was awful, and I don't know how anyone is using that piece of crap. Once Verizon/Samsung got off their collective asses and finally updated their GN to 4.2.2 I went back to stock and I've been much happier.

If a Nexus 5 gets announced, I will be buying it.

The only non-Nexus device I've ever considered is the One due to its extremely good hardware design, but as long as it has Sense UI on it, I will never ever go near it.

There's no way in hell I would EVER purchase a Samsung phone again. Especially a non-Nexus device. I recently had to help someone out with their S3, and the UI was an utter mess. The S4 looks even worse.

If no phone is announced soon, get the Nexus 4 or a used Galaxy Nexus. No question to me.