
I would have to go with Metroid purely based on the first game because that's the only game out of both franchises that I really put any legit time into. I've tried a bit of the Castlevania games and they are fine, but from what I've seen the Metroid brand seemed to have taken chances with different styles (a first person game, a pinball game, etc.). Now I could be wrong and Castlevania has done similar things, I really haven't kept up with that Franchise.