Bastion

Basically the most powerful Sentinel, Bastion is the next step humanity should take after X-Men: Apocalypse. Why would they do otherwise, after witnessing first hand the destruction an omega level mutant can bring?

Born out of the two most powerful sentinels, Bastion is incredibly strong and fast, able to fly, and completely impervious to psychic attacks. He can control any other sentinel, as well as any kind of machinery – but this isn’t all, since he can also transform normal human beings into Prime Sentinels.

Most interestingly, he doesn’t look like a sentinel, and this makes him able to blend into a crowd – which would make him an awesome hidden villain, able to strike at will and then retreat. He could occupy a position of power and, over the course of a couple of movies, he could completely obliterate the X-Men. But, of course, he would be stopped by a Phoenix, Jean Grey.