In-game, your opponents are a lot easier. They cannot make smart moves and use strategy, so you could beat the game with just about anything if you levelled up enough. Both Staraptor and Talonflame can be great, but in-game it really doesn't matter. Just attach some good moves to them and you'll beat the game in no time. Either would work fine.
If you want to use them for competitively, then you should find which one suits your team better (like working around type weaknesses of your team, for example). Competitive is a lot harder because your opponent can destroy your plans while also planning against you, and they are usually experienced and know what they're doing. Without a good strategy, they could win in a flash.This question that asks the same thing in a more competitive view can help you decide which you want if you decide to try competitive battling.
Hope I helped!