I would go with Garchomp. It has ridiculously high Attack, excellent Speed, and solid HP. Dragon and Ground together hit a great many things in the game neutrally or super effectively, including Raihan, Eternatus, and part of Leon's team. It evolves fully around the 7th Gym. Here's a set:
Garchomp @ Rocky Helmet / Dragon Fang / Soft Sand
Ability: Rough Skin
- Dragon Claw / Outrage
- Poison Jab / Iron Head
- Stone Edge / Fire Fang / Crunch / anything else
Keep in mind it doesn't matter all that much ingame, you can use whichever you prefer.
Hope I helped!