^ Omanyte and Kabuto both have the same type.
I always pick the Dome fossil whenever I feel like adding it to the team. I just like Kabutops over Omastar. The first time I've played through Kanto was the only time I picked the Helix fossil, but that was only because I forgot which Pokémon came from which fossil. I was disappointed when I got Omanyte, but when I decided to use him anyway, he was an awesome member of the team. After that though, I always go for Dome. Helix is cool, but still. Hail Dome!