Kyogre ( cause it is a legendary)
then there is other strong ones that you can get pre-elite 4 such as
Walrein, Golduck, Swampert( starter fully evolved), Starmie, Milotic ( very rare) Lanturn, Wiscash, Kingdra, Gyrados, Wailord, Ludicolo, Crawdunt
Any water pokemon that can evolve is potentially a strong pokemon to use. Using base stats Kyogre is the best with 670 and then
Milotic,Gyrados,Kingdra= 540
Swampert= 535
Wailord, Golduck= 530
Swampert or Wailord.
Rectha
i think slaking.
Roselia, Bellossom or Sceptile.
the best team for battle dome in Pokemon emerald is a grass type(against swampert , and a rock type(against charizard and salamance)
Swampert or Wailord.
Rectha
Kyogre.
Water.
i think slaking.
The best water type would be Kyogre but you can't get it in leafgreen you need to get one from sapphire or emerald other than that the best water Pokemon is blastoise.
Most water type Pokemon like tentacool.
Roselia, Bellossom or Sceptile.
In Sootopolis City.Trainers and Gym Leader uses Water-Type Pokemon.
the best team for battle dome in Pokemon emerald is a grass type(against swampert , and a rock type(against charizard and salamance)
The strongest dragon type in pokemon Emerald, Sapphire and Ruby, is the legendary pokemon Rayquaza. In terms of non-legendary pokemon, both salamance and flygon are strong dragon types.
if you mean the starter Pokemon for emerald it's treeko-a grass type, torchic-a fire type, and mudkip-a water type