You want to rotate them randomly, as this makes your test more reliable, and the better advert doesn’t necessarily have the best clickthrough rate (which is what Google would use to determine which to prioritise).

It’s a bit more complicated if you have matches from two different Adgroups. For example, if you are bidding on “Printers” in one Adgroup, and “Laserjet Printers” in another Adgroup. If the search was for Laserjet Printers, Google could show either advert. It’s generally accepted that Google will show the one with the better Ranking Quality Score, but to the best of my knowledge, nobody’s ever catagorically proven this.

I have a questions, if your two adverts are made of the same keyword list, how will Google decide which advert to show up upon a matching query, if the same keyword is found in both advert?

In your example, both adverts has the same text, and relates to Canon Pixma. If I search for that term, which of your adverts will show up? Is there a specific rotation system in place?