I'd say the most convincing evidence for aliens is the great pyramid. I'm not 100% sure it was aliens but there is evidence the pyramid would have worked like Nikola Tesla's tower that would have produced unlimited energy and could distribute it wirelessly. If the pyramid was used for this, the Egyptians surely would have documented it, but for as great of a feat building the pyramid was with it's 99% accurate angles, positioning, and proportions, it doesn't align with the stars the way it was intended. Instead it lines up with the constellations 10,000 years ago. Aliens would have used it as a source of energy for their spaceships. Maybe the key to technology to space travel is something we already know. After all, Tesla based his invention off the pyramid which would give free clean energy to the whole world. It was JP Morgan who pulled funding because his industries would go out of business if everyone had free energy. We may have the answers to a lot of our problems but people are hiding them from us for their own benefit. I heard a story of a man who built a water powered car who drove from LA to New York on 18 gallons of water. A couple of "investors" from Ukraine set up a meeting with him, but they ended up being hitmen from a gas company. They killed him and all evidence of his invention disappeared. This is another example of industry hiding the answer to a problem to save a business.