Shaymin, easily. No, I'm not just a pussy choosing the shrub Pokemon. Sky form Shaymin is deadly. I've swept teams of Rayquaza and Arceus with it. Search it up on Smogon and you'll see for yourself.
LATIOS TRADE ME POKEMON X IFNA (give me your friend code.) I'm trading a lvl 40 Suicune (special Suicune) for a Latios i'm srs.
Hm... Of all the legendary Pokemon, my personal favorite would be... Meloetta. It can be very, very deadly. Also, just as a clarification, the following are not legitimate legendaries: Latios/Latias Manaphy Phione Pretty much those. I am not sure if the regi trio and regigigas are not considered legendaries, but what I know is that they were fan based into legendaries by people who mistook them as legendaries because they could not evolve, and you could only get one a game. There is a reason they are allowed in OU competitive battling, which permits no legendaries or ubers.
#1- Lugia #2- Rayquaza #3- Mewtwo #4- Giratina #5- Articuno #6- Kyogre #7- Darkrai #8- Regigigas #9- Ho-Oh #10- Reshiram