Here's some more speculation FWIW.
I think the Europa-type of planet could be the best chance at harboring life because the protective ice shell will keep life safe from a number of cosmic hazards as well as create a large orbital range for life-supporting status. Even an eccentric orbit for such a planet could still support life which gives the potential of such a planet for having a large habitable zone around it's parent star(s). So a reasonably intelligent species of water dwellers could develop a civilization under such a blanket of ice and we would never hear radio transmissions from them and we wouldn't see any signs of life on such a planet with even our most powerful telescopes.
Actually SETI is not looking for intelligence per se. It is looking for a tool building species. (Indicates intelligence)
They might have life, but a water-based civilization would have a hell of a time becoming advanced for one reason: lack of fire!