What's the best fitness tracking app?

Amazing UI, more than fitness tracking!

I've used the whole gamut of fitness tracking apps and Strava works best for me. It tracks your run, your splits, your distance, calories, and a whole lot of other stuff that makes it fun to run. It also auto-pauses when you're at a traffic light or stationary for a bit while you're tying your shoe. There's a whole slew of features for a paid user, but the free user (me) gets a lot of the vital information for zero cost. Highly recommend Strava. 10/10 would download again.

Not exactly what you're looking for here, but I like using Healthkit. It takes the data I have from a number of different places (IoT Scale, Thermometer, Blood Pressure) as well as other apps -- Pillow for sleep, MyFitnessPal for calorie intake, etc and puts it all in one place for me and my doctor. Plus you can let apps connect to each other as well.

Check out: Charity Miles. It's not exactly what you described because it doesn't have great calorie data (or other data), but it's incredibly minimalistic and tracks walking/running/biking AND donates money to charity for your exercise.

Gives you a wealth of tools for tracking what and how much you eat, and how many calories you burn through activity.

Easy to use, includes most workouts, lets you save premade workout routines

I can highly recommend YAZIO. You can easily track your calories and enter your physical activity. You can also import data from other apps and devices like runtastic or withings. The app can be downloaded for free. It has definetly helped me to reach my goals!