Use Pokemon Showdown instead: http://pokemonshowdown.com
Cannot recommend this site enough. It's a Pokemon battle simulator for competitive Pokemon battles, and it's better than in-game battles in basically every aspect.
- Faster animation. In-game battles seem dragged out and long, but the Showdown animations are simple and allow you to play battles faster.
- In built teambuilder. No more grinding in the game, you can just choose your Pokemon from a list.
- Skilled opponents. While there are still some idiots with troll teams on the site, there are many more quality opponents on the site than in-game, especially once you increase your ladder rank.
- More accessible. You can use Showdown on many different platforms, but in-game is limited to the 3DS.
If the only type of competitive battle you've ever played is wifi battles, be prepared for a step up in difficulty and understanding rules. Some of the opponents there are very good. What you call "good" in in-game might be terrible in Showdown. Showdown also runs on Smogon's rules and tier systems. Do some research on this before you play.