One of the most common life-ending medical decisions is to end all curative medical treatment and to disconnect life-supports. Such life-ending decisions are taking place every day in every modern hospital. There is no controversy. And we assume that the safeguards already in place in each medical-care facility will prevent mistakes and abuses of this form of the right-to-die. Thus, whenever the patient is being supported by any form of medical technology, it is always a legal option to end that treatment and allow nature to take its course.
Yes, euthanasia is always better than withdrawing life support as respecting one's right to choose, i.e. consent, is always preferable to taking away one's right to consent and choose. Should a person wish to remain on life support, that should be their choice just as much as it should be their choice should they choose to end their life. Respecting the right to choice is of the utmost importance.
Euthanasia and withdrawing life support are about the same. People on life support are pumped so full of painkillers they really don't feel anything. Cutting off life support is essentially the same as assisted suicide--the patient simply falls asleep and never wakes up. Both are equally as sad in the end of life, but both medical procedures are valid forms of non-treatment for patients.
Withdrawing life support is supposedly not a painful way for people to go. Rather, we are doing what (in the past) would have been normal for someone dying, removing the nutrition and letting their body slowly shut down. In the past, people who were dying would not have been forced nutrition as they are now. I have been told by the medical community that this is a peaceful and humane way to let someone die, letting their body shut down in the way it is naturally supposed to go. Conversely, assisted suicide is a forced way for someone to die--and it could happen years before their body would normally shut down. While it may seem humane, it seems to trivialize a person's value as a human, seeming to imply that the elderly or sick are not worth having on Earth. This is a sad statement for society to make.
No, euthanasia is not better than withdrawing life support. In almost all cases, a party can act independently to take their own life (even though suicide is illegal) and therefore as a result involving anther individual would be an emotional and psychological burden that person would have to carry for life.