the best way to GET legendaries is by action replay.
and the best way to CATCH legendaries is lowering there hp and catching them.
or choosing the right pokeball:masterball,ultaball,repeatball,greatball,and pokeball.
it is scisor
Probably Weavile, Glaceon, or Mamoswine.
master ball
I'd say Garchomp, Gallade, Magnezone, Electivire, Magmortar, or Mamoswine.
the best type of ball to catch all legendaries is the ultra ball
Arceus or Spiritomb. It depends on who your going to fight.
Rayquaza/Groudon/Kyogre each are level 70 and the only legendaries. And Latios/Latias
in etrena forest
Throw a masterball at it.
most legendaries such as girintina, heatran, dialga, or arceus. my party is: dialga, palkia, heatran, girintina, and lugia. but i think the best Pokemon is a lvl. 100 ditto.
Master ball
You can catch more legendary pokemons on platinum. So you can catch more on Platinum, then the other games :)