Amazon GameCircle or Google Game Services? Or both?

When it comes to scores and achievements in your Android games, do you use Amazon GameCircle or Google Game Services - or both? I’d be interested to hear if you detect if the user is using a Kindle device and serve up the Amazon GameCircle and show Google Game Services for everyone else - or if you just pick one of the two. I just ported my iOS game which uses Game Center - I’m really trying to decide what the Android counterpart should be. Any feedback would be greatly appreciated!

My game is here:
https://play.google.com/store/apps/details?id=com.embraceware.shuttlescuttle&hl=en

Both in two versions of your app. Amazon Kindle Fire devices don’t have the Google services on them so you need to use Amazons GameCircle.