Re: stock music app or google play music...
I love Google Music because well, it's google, and the UI is aesthetically pleasing. But the Stock S4 music player has a layered and detailed interface, and has great lockscreen/homescreen/notifications bar widgets, unlike Google Music. Google Music's widgets often seem out of alignment, or inadequate in quick access features. Stock player also has that Music Square feature which I think is pretty nifty.
Even though I use Google Music 90% of the time, I still use the stock music app sometimes and I'm stuck between the two. If Google Music updates itself, I might say goodbye to the stock player.