So i Have just started, well 3rd badge. I want a good team as *weeps* i have never been able to complete emerald as well i dunno. I want suggestion from inside the game. so here it is:
Marshstomp
Beautifly} i dont want 2 flying types suggestions
Swellow}
Electrike
Numel
Aron
I no it needs work. as i said i dont want 2 flying types i was thinkin claydol/flygon but thats would be 3 grounds which is unstable. Please open to suggestions, has to be INGAME pokemon . .
this is my first time to this site sorry if i have posted in the worng place . .

Gardevoir makes an excellent special sweeper. In my experience, Aron and its evolutions are not a very good choice; they die easily to fighting type moves, even with their huge defense stat, and there seem to be a lot of fighting type moves used by the in-game trainers in Emerald. Your other team choices are okay, although I would remove either Beautifly or Swellow; not because they are both flying, but because they are both overall fairly weak pokemon. Flygon is a good pokemon to consider adding, it learns some very good moves and has good stats.

So i have swap a bitt how does this sound:
Swampert
Manetric
camerupt
Altaria
Hariyama
Arggon

looks decent- much better at the very least. I dislike altaria in emerald in-game but that is your choice

Keep the Aron! When you get it evolved twice its a super-powered steel type! Then look for an Absol. Its the only good dark type in-game.

And dude when u get a beldum keep it and put the exp share on it and evolve it into a metagross and you have aforce to be reckoned with.

But theirs a catch when getting Beldum. You have to had beaten the Elite Four.

Yeah it's godd to have a Metagross

Get rid of beautifly, and probably electrike. But the most important thing is, make sure all your pokemon can copensate for their weaknesses.

Don't use 3 or more of one type or else it will be unbalanced

lol, i seldom use a whole team and i beat the whole game by just using my starter (Charizard for FRLG and Blaziken for RSE), if you train their ev to the max and be a little bit hardworking in training your sole fighter, you should be able to solo the elite 4 for team, i prefer those pokemon with 2 really high stats, preferably over 350 at level 100 (e.g. hp & attack for blaziken), alakazam will do great as special sweeper, golem a tank (as you can get these 2 very early in the game), i basically chooses the ones with best stats. (check the psydex for the stats)

Your team is fine but you need to change some things.
Here's what I would recommend:
Marshtomp(or Swampert)
Manectric(owing to its high speed)
Torkoal(Super Defense, good atk and sp.atk)
Beautifly(make it learn silver wind)
Lairon(if you have evolved aron)
Hariyama(catch makuhita in granite cave and evolve it) or Swalot(get gulpin north of mauville and evolve it)
I hope this helps.