Having had an S3 (Jellybean 4.1.1) and now a Lumia 520, I like Android better. I didn't really notice any lag, and I rely on Google apps (Google Now, Keep, Tasks, Play (for music), Drive, Photosphere), some of which has no 1st or 3rd party equivalent on WP8. Personally, I like the look of Android better, the file manager, Calendar looks better on Android, more app selection, notification customization. there is a greater choice of browsers. I had Chrome, Firefox, Stock, Opera, and others, which I could sync with my desktop browsers. One thing I hope WP8 implements is better notification. I use 3 email accounts (Hotmail, Gmail, and Work). I can turn each notification on independently and have a different ringtone for each. For WP8, it's either all on or all off with the same tone.
WP8 is smooth and without lag. Not so much a WP8 feature, but I do appreciate the FM radio on my 520. I like how I can take pics w/out unlocking the phone, something I couldn't do on my Android. In time, the app selection will improve. I hope Google will develop some more apps for WP8. A couple annoying things on WP8 apps (at least for me) is that on Skype, I cannot attach messages whereas I could on Android. Also, a minor thing with the eBay app is that if one of my auctions ended, I could not relist it with the WP8 app. Yes, I could do it on the IE mobile browser, but it's annoying that I have to do that. Anyways, I am enjoying WP8 and hope that as the platform matures, some of these things will be improved.