Grendizer as a super robot is by far more powerful than any of the others.  Whether it's Great Mazinger, Getta Robo G, Danguard Ace, Shin Getter Robo, or even Mazinkaiser, Grendizer remains the king.

Hard to believe ?  Don't let these newer super robots fool you.  Just because they are newer, it doesn't mean they are any better.

Grendizer is distinct.

What makes Grendizer distinct from the rest is that he is a UFO robot; alien technology.  Grendizer was built with the outstanding and advanced science logs of planet Freed.  Planet Freed was a planet that did not partake in wars and dedicated all of its resources on science and technology.

When Vega decided to attack Freed, they took all of this science and used it to build Grendizer.  This super robot was to help Vega in taking over the universe as he planned.

Tell me, when a super robot is built using an entire planet's specialization, the science, what will you come up with at the end ?  Keep in mind what the aim of building this super robot was-to plunder the universe.

Grendizer, unlike the others, is not a stand-alone super robot.  Grendizer has its own Spazer saucer.  If anything was missing from the Grendizer series, then it would've been that this Spazer saucer should have been used more often.  The nice thing about Spazer is that when Grendizer is connected to it, it can travel at top speeds of mach 9.

Grendizer is also distinct in that it will not allow anyone other than Duke Freed to pilot it.  If someone else comes close to Grendizer, this person will get shot by Grendizer.