Let's say Mega Sceptile vs Mega Sceptile each using Dragon Pulse. Would it end up like Order Of the Phoenix, meaning the one with more power would win? This can be in the manga, anime or the games.
As stated before, in the games it would be chosen randomly.
The anime and manga is based around love and friendship, and stats and levels don't exist. Hence, no speed stat. It would be based upon however the creators decide it to make it.
Hope I helped. :)
I'm not sure about the manga.
In the Anime the Pokémon would use their moves at the same time and the one with more power will win.
In the games it will be random. If both Pokémon has the same speed it totally depends on luck and any Pokémon can go first.
The one with the faster speed would go first. It would be rare for them to have the same speed, but If they do, I'm not sure what would happen.
Maybe Pokemon added a scissors, paper stone function for this case. That last sentence was a joke.