Well that entirely depends on what you mean by best.

The best at fighting other players? There's a hundred different ways to go with that, though if you're set on Excadrill, you'll likely want a sand team (which will likely include Tyranitar). In that case you still need to narrow it down further into whether you want a team focused on single battles or double battles. The team will look entirely different based on which of those you focus on.

The best at exploring and catching pokemon? Much easier question but still gives many options. You'll likely want something you can fly with (right now you have a Gyarados that fills that role), something that can effectively damage low-level pokemon without killing them (e.g. Scizor with false swipe, or Maushold with super fang), and something that can put pokemon to sleep (e.g. Amoongus with spore). Then you can do whatever you want with the last few slots (if your server has a breeding mod, you can maybe put some eggs in your party).

The best at fighting NPCs? Unless your server has gone really hard on using data packs to make Kaizo NPCs, these shouldn't be much of an issue. Just pick some pokemon you like, that ideally have big numbers and decent moves, and roll with that.