Rayquaza is a Dragon/Flying type, which again is a common typing, but on Rayquaza, it is also a pretty solid typing for it, as well Rayquaza has an amazing design, like it's pretty near to being perfect. Now, we all know Rayquaza is literally like one of the best Pokemon out there in terms of battling capabilities as it has amazing stats, some solid abilities & a pretty darn awesome movepool (then there is Mega Rayquaza which well doesn't need to be talked about) Overall, I love Rayquaza and this has always been my go-to legendary in the generation 3 games, but I ranked it at this spot just because don't really get to use it until pretty much near post-game, and I'm not big into Ubers with competitive, so I have used this before, I just don't have much time with using it to form as great of a connection compared to the others.
I guess Flygon for the win