You are also guaranteed more balls to throw because you need less raiders and you can pick the color gym you want...having said that, my catch rate has slowed after a 5/6 start. However, only one I've thrown at that I was sweating about was today, 2070...14/14/15 missed it. I went completely through Entei throwing pinaps, surely wouldn't try that vs Rayquaza
Is Rayquaza the easiest legendary to catch?
For me, it’s the easiest legendary to throw on because the circle doesn’t really move and it’s a high (but not far) throw.
Also, as opposed to Kyogre and Groudon, you should get a double catch bonus for flying and dragon medals.
What do you guys think?
Managed to get to 90%, we will see if I can maintain that.

Answers
I agree with Mr-ex777, I thought it was very easy early on, after going 2 for 2. But its much easier to hit than keep and very few people I know have a good Dragon medal. Ho-oh had dual typing and Psychic/Fire is much easier than Flying/Dragon.
Maybe it just seems easy after Kyogre. Groudon was the easiest of the three, for me.
If you have gold Dragon medal, a good team to get always +3 damage premiers and always manage to have the gym on your team's control, then it's easy to catch. Personally I don't always got excellent throws on it when it's not flying. I feel more confident when he's up. 12 seen 8 catch for me and best I saw is 93% 15/14/13.
Of the three recent Legendaries, I found Groudon to be the easiest. When I consistantly hit him with Excellents he'd always end up caught, RayRay on the other hand has been the total opposite. However, I have a good catch ratio with Ray' so far so I can't complain. Overall he's annoying more than difficult whereas Kyogre was both annoying and difficult.
Groudon
Seen: 23
Caught: 19
Kyogre
Seen: 23
Caught: 11
Rayquaza
Seen: 21
Caught: 16
The easiest Legendary overall to catch: Mewtwo.