I would suggest Gyarados. It’s extremely easy to obtain a Magikarp. They’re everywhere. You can then let it piggyback on your team till it evolves. This is my suggested set for Gyarados:
Gyarados @ Anything
Ability: Moxie( If you can get it)
Evs if you’re going to Ev train: 252 Atk/ 252 Spd / 4 whatever
Preferably an Adamant Nature, but it doesn’t matter
- Waterfall
- Dragon Dance
- Ice Fang / Crunch
- Earthquake
Dragon Dance then sweep everything. Waterfall is powerful STAB. Earthquake is really nice coverage and Ice Fang is also pretty necessary, but Crunch can be helpful. The great thing is you can relearn moves whenever you want, so you can swap Ice Fang and Crunch depending on what you need. Hope you found this helpful!