odinmode

Impetus is very good and completely customizable. If you just want something simple to do standard intervals consider checking out my app. It also includes Google Fit integration which I believe is a first for any of the android timer apps. https://play.google.com/store/apps/details?id=com.odinmode.android.interval.timer

I created an app for this exact purpose and I believe it to be the easiest to use out of all the available apps in the market. It also includes integration with the new Google Fit platform to make tracking your workouts super easy. Download for free@ https://play.google.com/store/apps/details?id=com.odinmode.android.interval.timer Impetus is another really well designed app if you need more customization in your workouts. Let me know if you have any questions about using either one and best of luck!