What is the easiest way to unlock???

[jnfs2014]

For me it is the SSE on easy.

[SkyMyl]

...unlock what exactly?

[jnfs2014]

characters.

[SkyMyl]

characters.

Lucario: Go through Classic on Very Hard or Intense to get Target Test Lvl 5. Beat the other ones with one character on Target Test.
Luigi: Classic Mode method.
Captain Falcon: Classic.
Ganondorf: Classic.
R.O.B: Used the VS Mode method.
Ness and Marth: Vs Mode method.
Sonic: Unknowingly used the Vs Mode method.
Falco: 100 Man Brawl with a friend.
Toon Link, Wolf, and Jigglypuff: SSE.

That's how I unlocked them. But SSE is the easiest method.

[Kilroy]

I think I used vs. matches with everyone except Toon Link...

[Dawei]

Go to special brawl, set it at flower lightning stamina, and set stamina at 1 for your opponent, and any number higher for you. Then just mash the start button.

[Lotos]

SSE.  No fights; long as you pass, you get the characters (except those last three).  I did the alternate methods except for R.O.B.  (I had 249 trophies, needed coins, went to VS mode, went from 151 to 160 matches...)

[Macawmoses]

Pretty much answered every way possible; further questions can be pm'd to me :)