In the deep and honorable traditions of the Japanese nation, there is perhaps none so wonderful as the bond between little boys and giant creatures, whether natural or artifical. Time and time again, Japanese movies such as Godzilla vs. Megalon and Gamera have shown us that there is no better place for the horrifying powers of these beasts to rest than in the capable hands of spunky children. Unfortunately, I think the answer to this question is fairly obvious, hardly worthy of an entire debate. All you have to do is look at the recent rash of cybernetic puppies, kittens and raccoon sales to realize that little Japanese kids love robots. Think about it.
Monsters are just too limited.
On the other hand, a giant robot is a rainy-day pal who can perform trillions of fun activities per CPU cycle with no maintenance required. No, the choice is elementary. Monsters may be okay for your average Joe, but there's no way a little Japanese boy is picking one over a wicked cool robot. Think about it, you're a young Japanese boy. You've got everything you could ever want already, video game systems, motorized dogs, ramen noodles, tiny, tiny, tiny little shorts.