We've done Teppanyaki and Coral Reef with our trio (ages 3,6,and 8). Personally, while the kids did enjoy the fishies swimming 'round, dh and both agreed Japan's food was much better. We had 5 pm seating @ Coral Reef (party of 8 -- had my SIL, BIL and my 3 yr old nephew). We didn't get to sit right at the tank, but about 8-10 feet from it. It didn't hamper our view, except for my poor SIL, whose view was largely obstructed by a pillar. Divers were in the tank while we ate. I recall that the kid's menu had pasta and pizza and I think chicken nuggets (the pizza looked yucky -- very frozen-reheated looking, but pasta seemed ok.) My 2 yr old LOVED my lobster bisque... however -- we later discovered that the sauce used on the Seafood Pasta at Chef Mickey's was essentially the same, really couldn't tell a difference, although admittedly I didn't have them side-by-side to compare. I will say CM's was a lot cheaper, though!! The big drawback for us at Coral Reef was the price -- by WDW standards, even, we just thought it was over-priced for what we got. Teppanyaki was more in-style for my dh, too, as it's steak/chicken/shrimp and rice. Coral Reef had lots of items in their dishes that my simplistic dh would wrinkle his nose at! (He did eat his wasabe potatoes, but the word alone really scared him!) If you like Benihana's and such, you'll like Teppanyaki. If not -- well, your choice got really easy, huh! My kids still have their chopsticks that the waitress "rigged" with rubber bands and a paper wedge to make chopstick "tweezers" for easy use!
Either way, you will have an excellent meal -- we just happened to prefer Teppanyaki, and if we did CR again, it would just be for dessert for a brief look at the fishies.
CIndy