I use both Amazon Cloud player and Google Music player on my Android phone, each having its good (Amazon's lock screen player is a lot nicer, Google keeps track of played and thumbs up/down) and bad. But one thing I just discovered will make me use Google's player a lot more from now on: I just found a way to "sync" my playlists directly from the web client. Maybe it is a known feature but I just figured it out so it's new to me.
To do this, create a playlist in the web player. Go to the playlist on the phone and check Available offline - all songs in the playlist will show up on the phone next time you sync. Nothing earth shattering up to here. The cool thing is that if you now go to the web player and add/remove songs to/from the playlist, next time when you sync, they will be added/deleted on the phone as well. Very simple and obvious but also very powerful.
I used to download my Google Cloud music, added it to iTunes and sync to the phone using the awesome iSync. But now there is no more need for this. I will keep syncing my iTunes music via iSync but the Google Cloud music will stay only on the cloud.
As far as I can see, Amazon doesn't have this feature; well, you can set it to automatically download all your purchases to the phone but this is not the same, I just want some songs, sometimes old ones, not all the new ones. Overall this means I will be using Google's player a lot more from now on.
As a side note, I am using the paid version of Rocket Player by the same authors as iSync and love it. Too bad it doesn't play Google Cloud songs. But someday it will and then I will sync the playlists as I just said but not use the Google Music player anymore, Rocket has so many more features.