This is what I recommend for a normal playthrough
Swampert with
:
Ice beam
Dive
Surf
Mud shot-can be changed for earthquake
Swellow with
:
Aerial Ace
Fly
Steel Wing
Agility or Double team
Breloom with
:
Sky Uppercut
Giga drain
Leech Seed
Mach punch or Bulk up
Manectric wtih
:
Thunderbolt
Thunder Wave
Spark
Bite
Hm slave Pokemon
Camerupt with
:
Earthquake
Flamethrower
Eruption
Heatwave
Thats all I can say as its what I used on mine and I won the elite four with them when they were only lvl 50
Btw if you are on emerald you can change swellow with Rayquaza with the moves of Aerial Ace, Dragon Dance, Dragon claw, Fly
If your on sapphire you can swap swampert with Kyogre but I heavily recommend on searching what's the best moveset for Kyogre as I don't know his moveset very well
for Ruby swap out camerupt with Groudon and same with Kyogre I don't know much about his moveset
I know the movesets for rayquaza because I saw a vid about it
I never use legendarys because I want the challenge to be harder but if you want to use them I'll say to search them up
I hope you like my recommendation!