Where is the best place to train Pokemon by level in emerald?

in Pokemon emerald

i use the Pokemon league

you have to use the exp share and (optional) the switching the Pokemon you want to train out of battle

im training my milotic

what i do is put him in front

1)he goes into battle

2)i switch him out

3)kill

4)then i switch him back in

this way, he gets 3/4th of the total exp (3/4th of 2000 is 1500)