There are some essential oils that can be used therapeutically if you are careful For example, I frequently recommend eucalyptus essential oil in a capsule along with horseradish, thyme and chaparral powders to treat pneumonia and bronchitis. Usually takes no more than 3 day to clear up the infections. The nice thing is that the oils are specific to the respiratory passages, so they will not cause secondary infections like antibiotics. Dose is still critical though. I recommend 8 to 10 drops in a capsule 3 times daily for adults. And never for children. I took 15 drops once without any ill effects, but this was still pushing it.
I have had aromatherapists jump all over me in the past for recommending EOs internally. What they do not seem to understand is that we ingest EOs on a daily basis. Many of them, such as orange, are used as flavoring. And many others we get from the spices we eat.
There are some very dangerous EOs though, such as Wormwood and tansy, so you need to really do your homework first.
As for Young Living oils being the best, I guess that would be a matter of opinion. One aromatherapist I talked to actually said that they were extremely poor quality. I have never used them. I buy my oils from wholesalers I trust. One EO line I refuse to use though is Aura Cacia.