Throughout the franchise of Pokemon, and in each generation, Nintendo has designated several Pokemon to be classified as Legendary, and thus the best of the best. Here are my picks for the best Pokemon classified as legendary.
1. Mew
Although its not very powerful, it is technically one of, if not, the very first Pokemon. Its also adorable, and it looks like a kitten. Its probably one of the hardest legendaries to find and catch. I have never caught a Mew, sadly.
2. Zapdo
Electric types rock, and so do flying. The second of the legendary birds, Zapdos is encountered at a high level, and is definitely fun to use. It is a good counter against any water types, and can also be useful against ground types, since it is also a flying type.
3. Regigas
I stated earlier that Mew was one of the hardest Pokemon to catch, but Regigas is right up there too. In order to catch it, you must have three other legendaries caught, and its insanely powerful as well. This Pokemon might warrant the use of a Master Ball in my opinion.
4. Lugia
One of the two tower Pokemon, Lugia is pretty powerful, and has a great backstory. It also appears in Pokemon 2000, and plays a significant role there.
5. Latios
A very awesome Legendary Pokemon, its very fast, and has some pretty awesome abilities in battle.
6. Dialga
This Pokemon is a powerhouse in battle, and is one of favorite offensive Pokemon to use. It is one of the more modern legendaries known as a mythical Pokemon.
7. Suicine
I'm not a dog person, but this Legendary Dog is pretty cool. I have a thing for pairing water and electric types together, and I often battle with my Zapdos and my Suicine together in dual battles. It is almost as fast as Zapdos, too, so I almost always get first moves!
8. Groudon
Groudon is the first member of the Weather Trio, and is arguably the most powerful Fire type Legendary out there. It isn't very fast at all, but what it lacks for in speed, it makes up for in brute strength.
9. Kyogre
The polar opposite of Groudon, literally. Its faster than Groudon, and as a water type is great to pair with electric types. It is a favorite to use in tournaments with a Raichu beside it.
10. Mewtwo
The very first time I used my Masterball was on a Mewtwo in Pokemon Red. Mewtwo is insanely powerful, and has great stats. It is also a sentient, talking Pokemon, so it has a personality.
11. Rayquaza
The best legendary Pokemon ever. Period. It is a dragon and flying type, which makes it immune to almost all types of attacks by almost all Pokemon. Its also very cool looking, and has a great attack set. This Pokemon is also granted a mega evolution in Gen VI which somehow makes it even better.