They are both unique for their own reasons. Both Coral Reef and Sci-Fi are must do's on our trips. My son is 10 and asks for both of these restaurants when we are planning.
If your group really enjoy marine life, then eating next to the enormous floor to ceiling aquarium at Coral Reef is amazing.
Sci-Fi is just overall fun environment with the old move trailers playing while you dine in your pretend drive-in car. It's also one of the coolest and quietest places in all of WDW which makes for a very welcome break, especially on a hot summer day.
Food wise, there are not a ton of non-seafood selections at Coral Reef. I usually get the striploin and it's always been pretty good. But if steak of seafood aren't your thing, then Coral Reef wouldn't be a good choice. Where as Sci-Fi has more diner type food that will likely satisfy a wider audience. You can always check the menus to see which is more appealing.