You do realize, that even if humanity went with the Amazon-like aliens, that if they're really close to extinction, it wouldn't be too hard to, you know, kill them off. Here, imagine this: Humanity helped them wip out the peace loving aliens, however, we have come to understand this race's nature. We know that, sometimes down the line, they might attack us. So, after we gain the gift of their technology, we, being so gracious, give them a stockpile of our own weapons and a large amount of food. The weapons are not for any other reason than the fact that they are low on their own weapons, and need time to make more, so our shitty human weapons will at least give them some extra defense in the mean-time. Concealed in the food are very[/i[ slow acting poisons, and concealed in the weapons is/are a nuke/nukes that re set to go off. They leave, and than the nukes go off. If none survive, great, this race was just killed. If not, those left will be in a severely damaged ship. They will have no shoice but to eat the food we gave them, as it will be a long hourney back to their own planet so that they can restockpile and than get revenge. However, the poison kills off the survivors.
Also, I choose the peace loving aliens. Mostly because I love technology and peace, and peaceful aliens are most likely thinkers, so they probably have an overall better technology, instead of just tech for war.