Aside from it thinking one Aquabats album art belongs to most every song on my phone, I like Google Music. If for no other reason than it gives me access to the ~90 gigs of my full music library anywhere I have a connection or I have the option to just play the stuff on my internal storage. It's a little more difficult to navigate than the OEM music player on my Atrix 2 with 2.3.6, but that could just be because I'd been using the 2 for ~8 months and just recently had to lose it.
I use Double Twist on the pc to get all my music then sync to my Atrix HD. Then I either use Double Twist or Google Play to play my music/podcasts on the phone. I like Google Play because it has an equalizer.