3)Aldnoah Zero

This Anime is about a war between people on Earth and Mars using robot technologies, even though Gundam is the first mecha anime I watched but i'm like aldnoah zero more.

Anime Synopsis:

The human race was once able to teleport to Mars after discovering a hypergate on the Moon. Those who opted to settle there discovered a far more advanced technology than that of their home planet, which they dubbed "Aldnoah." The Vers Empire of Mars was founded as a result of this revelation, along with a declaration of war against the "Terrans," those who remained on Earth. A conflict on the moon, subsequently dubbed "Heaven's Fall," caused the hypergate to rupture, destroying the moon and forcing the two worlds to agree to an uneasy truce.

Their truce, though, was precarious. After fifteen years, high school student Inaho Kaizuka witnesses the assassination of Princess Asseylum Vers Allusia of the Vers Empire, who had come to Earth in the hopes of restoring the empire's ties with its motherland. The armistice is broken, and the Martians declare war once more on the Terrans. Inaho and his comrades must now fight the Vers Empire to end the conflict once and for all in the face of this formidable foe.