In Pokémon Go, Rayquaza's best moveset consists of two moves. Those two moves are Dragon Tail, and Outrage. There are a few reasons for this. First, Dragon Tail is a fast move, meaning players will be able to use the move faster than normal. Dragon Tail is also Rayquaza's strongest quick move in terms of base damage. Secondly, both moves are dragon type moves. Rayquaza is a Dragon/Flying type, meaning it's vulnerable to Fairy, Ice, Rock, and Dragon-type moves. Since dragon-type moves aren't typically weak to most types, having two dragon moves is a safe bet.
Pokemon Go Rayquaza Best Moveset Explained
On top of all of this, compare all the other moves that Rayquaza can learn in Pokémon Go to Dragon Tail and Outrage. Air Slash is the only other quick move that Rayquaza can learn. Aerial Ace and Ancient Power are both good moves. However, they're weak in terms of base damage compared to Outrage and have more type disadvantages. The TM Hurricane makes a strong case for being in Rayquaza's main move. However, that requires a player owning the Hurricane TM in the first place.