Emerald help.

[The King of Nidos]

Hey guys I have a question. Where's a good place to train your pokemon after the E4 up to 100 on Emerald?

 

[VibuzeSG]

Depends. If you're trying to EV train, there are certain specific regions to look into, as you'll have to defeat certain Pokemon.

However, if just leveling up is all you are looking for, you can always fight the Elite Four over and over and over again. This is also a good way to earn extra money. There's also always the Sky Pillar, which has some wild Pokemon at high levels.

EDIT:

Spoiler

I just remembered as well, there's also the "True Champion"--after you fight the Elite Four you can find Steven Stone in Meteor Falls. If you talk to him, he'll challenge you, and his Pokemon are the highest levels of any in that game.

 

[Scarlet Devil]

exactly, what I do is, I only send 2 pokemon with me to the Elite 4, depending..... sometimes even 1......
anyways, the best place to go is fightin the E-4 again, or battle the Gym Leaders over, if their ready

 

[~Piika]

The Trainers' Eyes/Match Call trainers also give out some pretty good stuff if you're willing to walk around and don't feel like battling the Elite Four. Especially the guys around Route 117 and 110.

Though if you're looking for the most efficient, then off to the Elite Four you go.