Kepler-62f: best bet so far, but we’re just getting started
Space.com: Kepler-62f: A Possible Water World
“Look at our own ocean — it is just absolutely full of life,” said Bill Borucki of NASA’s Ames Research Center in Moffett Field, Calif., leader of the team that discovered the two exoplanets, in 2013. “We think, in fact, life [on Earth] might have begun there.”
The key to a more advanced civilization, however, may lie in pockets of dry land. Technology (as we would understand it, at least) would be difficult to develop unless any alien creatures could work out of the water.
That’s the kicker, isn’t it?