A squid tank needs to be huge and cylindrical, since they are open water predators. I haven't heard of anyone succesfully keeping squid (not to be confused with little bobtailed squid from Hawaii). An octopus would be slightly easier than a cuttle as far as feeding in my opinion, although the tank needs to be escape proof. This is not so for a cuttle. Both cuttles and octos require expert care however- a rule of thumb I tell people is if they can't succesfully keep a reef tank, forget about an octopus.