I think that Blastoise is the better choice. Gorebyss has better attacking stats and a great defense, but Blastoise has a good bit more HP than Gorebyss and has high and balanced defenses, whereas Gorebyss is only high in the defense stat and so-so in the Sp. Def. stat. Blastoise also has decent speed, unlike Gorebyss. Gorebyss has good psychic attack coverage and can learn shadow ball. But Blastoise can learn moves like Earthquake, Brick Break, Flash Cannon, and Dragon Tail. Blastoise can also learn Iron Defense. Also, as you said, Blastoise is a rapid spinner, and that's usually very important for getting rid of stones, spikes, and toxic spikes. So looking at the stats and movesets, Blastoise is better all around.
