It's always better to train players yourself. That way you're able to mold them and develop them as you'd like by focusing on the white skills. This is the reason the majority of advanced managers purchase low quality fast training players and train them themselves. For you information, players coming out of the youth academy are not fast trainers, and thus requires more rest packs/resources to train to the same standard as fast trainers. Bear that in mind when you allocate resources towards players from the youth academy. If you need a training tool to better estiamte the outcome of a given training session or better understand which combination of drills is best suited for your player, check out the power training tool I've developed in my signature.
Also, landing on 99 % is kind of risky from what I understand, as you might be drawn against managers one level above you. It's better/more safe to aim for around 90-92 %.