I like the third one, of the water falls. Looks nice. Here is something for my city, its called the Big Nickel lol.
Some (low quality) pictures from my vacation, went to Niagara Falls! (this was in Toronto) I took loads of pictures of the actual waterfall too but they're not on this computer. I'll try to post them here whenever I get the opportunity to. Sadly I wasn't available to get their later in the night for the Illumination of the Falls so no pictures of that.
Of the ones you mentioned I think The Iguazu Waterfalls and The Great Barrier Reef look amazing, although I've never seen the Grand Canyon like that. Any time I've seen it in pics it's always barren and red lol.
The place to be is . . . Snowdonia National Park - a place of outstanding natural beauty in the Principality of Wales.
It's hard to say just looking at pictures, which by the way, are beautiful! But I read somewhere recently that the Grand Canyon is officially on the Top 10 list of natural wonders. I recently got a library book titled "The Four Corners Region" so I can plan my visit there. I vote GRAND CANYON!