Are you trying to decide between updating a phone now, or waiting for the 5s release because of iOS 7?
I'm trying my best to leave Sprint ASAP. I am pretty certain that I want to join T-Mobile b/c they are rock-solid in the area where I'm moving to (Phoenix). I've used a ton of phones and platforms over the past 2 years: Blackberry, Windows Phone 7.5, iPhone 4, iPhone 4S. For the past 6 months, I've been using the Galaxy Nexus.
Thanks to my experiences with all the major platforms, I've formed a pretty comprehensive opinion on using them. First of all, I kinda sorta detest Android. Slow, heavy, and buggy. Only tangible value added over iPhone is Google Now and an awesome Gmail experience. I loved the iPhone 4S, but I found iOS SOOO boring. But, then again, I really miss having a buttery smooth OS experience that only iOS and Windows Phone can provide.
It is an annoying time right now to be signing up with any carrier, since the 5S is only months away or (if I go that route) Windows Phone devices will likewise be coming out with the Snapdragon 800 SoC, which just came out yesterday and outperforms pretty much everything currently on the market.