I was originally going to look on the Apple store and do some quick comparisons, but then I realized that data is only telling half the story. I personally like zero very much, Combined with my Fitbit app. There are certainly quite a few combinations you can use! Perhaps download a few and try them in parallel for a week (which is a little annoying because you have to re-enter your data a lot), but that might give you a good handle on which one you like best
The best I found was iFasting only because it told me what I wanted to know in a simple manner: what time is breakfast. I dont need a countdown. That and I could turn off most notifications. Not sure how popular it is.
https://play.google.com/store/apps/details?id=com.ibuild.ifasting
Now Im just winging it with a desired window of 9am to 3pm. I dont worry if its not perfect.