I currently own more smartphones than a person should be allowed to own. Among them: Samsung Galaxy SII Skyrocket (Android), iPhone 4 (iOS), Lumia 520 (WP8).
I've owned numerous Android phones starting with the original G1. I love the customization options for Android. I didn't love the poor battery life or the degrading performance. In order to eek out tolerable battery life and performance, I had to spend a lot of time tweaking and experimenting. Although there was improvement, the results still weren't great.
I switched to an iPhone 4. Battery life and performance was and still is amazing (running iOS 5). But it seemed like using the iPhone as a phone is an afterthought. No indicator lights... if I received a call or txt msg when the phone was not with me, there is no visible way to know it without turning on the screen. Lack of customization was another issue.
I then saw the Lumia 520 for $67 (no contract). I was a big fan of the Zune and know that much of the Zune HD's UI design found its way into WP8. So I wanted to give it a try. I've been using it as my primary phone for 2+ weeks. I'm getting battery life that is nearly as good as my iPhone (2-3 days between charges), performance that is fluid and crisp, and the ability to configure the screen with live tiles that provide me with the information that I feel I need to have on the phone's main screen.
This is using a StraightTalk microSIM, YMMV.