Hi amiga. I think Heathrow is an awful airport and you can be subject to many delays for luggage, immigration, etc.
Schiphol, Amsterdam is a lovely airport. I'm there on average once a week. If I remember correctly you would arrive at about 5pm and your connection to Edinburgh is from Gate D6 at about 9pm.
The likelihood of requiring an x-ray there is also very low.
Good luck!