Ask HN: Google App Engine or Heroku for my first Android app backend?

Hi, I'm going to publish my first free Android app to improve the schedule bus in my city. My app needs an API so I need a backend server. Since I won't have revenue for my app, I need a free hosting. My requirements are the next:

* MySQL database (or similar). Less than 10 MB.

* Cron. One task per day (less than 5 minutes per task).

* My backend is written in PHP. But I think I could translate into Python.

* No storage needed (just for the source code, a few json configuration files and the database). No photos, no images, no videos.

* Traffic. This is quite difficult to predict. Some context:

My city has approximately 80000 habitants.

I'm using Android >= 3.0. So this reduce the total amount of potencial users.

Ideally the app just has to connect once a day, the data will be stored locally.

The total size of the downloaded data (json files) is about 10kb (two or three requests).

Ideally the user will use the app like this: wake up in the morning, check the arrival time for the next bus to go to work and at the end of the day check again the arrival time to go home (very simplified, but the average user has the same routine: home->work->home). Anyway, just one request in the day is needed because I store the downloaded data locally. There is another use case where the user sends data to the server. I'm not going to explain it, but the data sent is just text (an arrival time) and is optional.

There is just another app like mine in my city but, in my humble opinion, mine is better :)

I have never used GAP/Heroku and I've read the usage and billing for both, but I'm still a little lost.

Thanks and sorry for my English.